Descry
The Descry is a recurring symbol in Path of Exile. It is most commonly associated with Innocence and the Order of the Templar.
Lore
Eramir in Act 2 mentions this about the symbol in the Fellshrine Ruins:
The Fellshrine is a shadow of what was once good in Wraeclast.
That sigil etched into its stones? It's a Descry, from when the Templar truly stood for something. To the ancestors of Oriath, the Descry was a flickering torch in the night. A source of inspiration and comfort.
Sad thing about torches... they go out.
The upside down Descry is commonly associated with Sin.
Initially, there was very little canonical information of the symbol itself. Its use was more general, being depicted outside of Templar-associated things, but eventually re-canonized as the symbol of Innocence since The Fall of Oriath, while the modified variant (the middle bar split) is the symbol of Sin.
"Descry" is an old word meaning "to catch sight of" or "to discover"[1].
Usage
The descry is featured on Path of Exile's microtransaction points, where they are the only symbol on a gold coin.
Active skills
A modified Descry is shown above the player when they invoke the 
Immortal CallImmortal CallSpell, Duration, Guard
Level: (1-20)
Cost: (21-36) Mana
Cooldown Time: 3.00 sec
Can Store 1 Use(s)
Cast Time: InstantRequires Level 34Take less Physical and Elemental Damage for a short time. Consumes up to 5 Endurance Charges to lengthen the buff and further lessen Physical Damage taken. Shares a cooldown with other Guard skills.Base duration is 1.00 seconds
20% increased Buff Duration per Endurance Charge removed
This Skill's Cooldown does not recover during its effect
(25-34)% less Elemental Damage taken
(25-35)% less Physical Damage taken
15% less Physical Damage taken per Endurance Charge removed
Additional Effects From 1-20% Quality:
(1-20)% increased Cooldown Recovery RatePlace into an item socket of the right colour to gain this skill. Right click to remove from a socket.
skill.
Another modified Descry (with the middle bar split) is shown above the player when they invoke the Immortal Call that have Dark Immortal Call mtx.
The Descry is overlaid on the shield of a character using the 
Tempest ShieldTempest ShieldSpell, Lightning, Chaining
Level: (1-20)
Reservation: 25% Mana
Cooldown Time: 1.00 sec
Can Store 1 Use(s)
Cast Time: Instant
Critical Strike Chance: 6.00%
Effectiveness of Added Damage: 220%Requires Level 16Enchants your shield with the power of storms, which lashes out to deal arcing lightning damage to attackers when you block them.Deals (38-896) to (115-2688) Lightning Damage
Chains +1 Times
Buff grants +(18-25)% Chance to Block Spell Damage while holding a Shield
Buff grants Immunity to Shock
Additional Effects From 1-20% Quality:
(2-40)% chance to Shock enemiesPlace into an item socket of the right colour to gain this skill. Right click to remove from a socket.
skill.
The Descry is projected onto the ground around a Vaal Totem with the "Allies cannot die" aura.
ZealotryZealotryAura, Critical, Spell, AoE
Level: (1-20)
Reservation: 50% Mana
Cooldown Time: 1.20 sec
Can Store 1 Use(s)
Cast Time: InstantRequires Level 24Casts an aura that grants bonuses to damage and critical strike chance of spells to you and your allies, and gives a chance to create Consecrated Ground against stronger enemies.+(0-1.9) metres to radius
You and nearby Non-Minion Allies have a 10% chance to create Consecrated Ground on Hitting a Rare or Unique Enemy, lasting 8 seconds
You and nearby allies have (20-39)% increased Spell Critical Strike Chance
You and nearby allies deal (10-15)% more Spell Damage
Additional Effects From 1-20% Quality:
(2-40)% increased Area of EffectPlace into an item socket of the right colour to gain this skill. Right click to remove from a socket.
uses the Descry in its skill icon.
Environments
Although there are a few patterns and the occasional face carved into the stone of The Fellshrine Ruins, there are no symbols except for the one directly above the entrance to The Crypt Level 1, where a figure is depicted holding a shape with three vertical lines and two curved lines.
The Descry is prominently displayed on one of the notes on the Noticeboard in each town.
The Descry is carved above the entrance of the Catacombs in Sarn.
Various areas of Act 5, 10 and the Epilogue are decorated with the symbol. In the lore these areas are part of the Oriath.
Consecrated Ground
A slightly-modified Descry (with the middle bar split) is part of the Consecrated Ground effect.
It also shown in the 2D art of the 
Sulphur FlaskSulphur FlaskLasts 8.00 Seconds
Consumes 40 of 60 Charges on use
40% increased DamageRequires Level 27Creates Consecrated Ground on UseRight click to drink. Can only hold charges while in belt. Refills as you kill monsters.
which creates Consecrated Ground, but not-modified (without the middle bar split)
The icon of the passive skill Sanctuary has a slightly-modified descry symbol on it.
Quest items
The 
Sign of PuritySign of PurityWrought from blood and gold, Innocence fashioned a weapon of tempered purity,
capable of banishing darkness, and bringing order to the chaos in men's hearts.
is similar to the Descry symbol.
Unique items
- The descry is featured on the striking faces of
Chober ChaberChober Chaber
Great MalletTwo Hand Mace
Physical Damage: (129-137.6) to (264-281.6)
Critical Strike Chance: 5.00%
Attacks per Second: 1.25
Weapon Range: 1.3 metresRequires Level 40, 104 Str30% increased Stun Duration on Enemies+1 to Level of Socketed Melee Gems
+1 to Level of Socketed Minion Gems
20% reduced Strength Requirement
(200-220)% increased Physical Damage
25% increased maximum Mana
Minions have (20-40)% increased maximum Life
15% increased Skill Effect DurationThe faithful may continue to serve, even after death.
. Elreon, Loremaster, a Templar, himself wields Chober Chaber. - The shield
Zeel's AmplifierZeel's Amplifier
Polished Spiked ShieldChance to Block: 26%
Evasion: (111-131)
Energy Shield: (83-107)
Movement Speed: -3%Requires Level 49, 64 Dex, 64 Int+5% chance to Suppress Spell Damage(40-50)% increased Spell Damage
+(60-80) to maximum Energy Shield
+(50-70) to maximum Life
1% increased Area of Effect per Enemy killed recently, up to 50%
You have Zealot's Oath if you haven't been hit recently"Great minds wish to reveal all the secrets of time and space.
But it does not matter.
Creation, the act of Matter Metamorphosis, is the only secret worth discovering."
- Zeel, Vaal Tinkerer
has the aforementioned modified Descry on it. - The amulet
Crystallised OmniscienceCrystallised Omniscience
Onyx AmuletRequires Level 61+(10-16) to all AttributesModifiers to Attributes instead apply to Omniscience
+1% to all Elemental Resistances per 15 Omniscience
Penetrate 1% Elemental Resistances per 15 Omniscience
Attribute Requirements can be satisfied by (15-25)% of OmniscienceThat winter, scorched refugees emerged from the shrine,
speaking only in strange tongues. They prayed to a new
symbol of power, not out of love, but out of fear.
is shaped like the Descry.
The Searing Exarch
The Searing Exarch, despite being an entity originating outside of Wraeclast, prominently displays a symbol very similar to the Descry. From the flavor text of unique items dropped from The Searing Exarch and the unique relics from the Forbidden Sanctum, the clues suggest this is the true origin of the Descry.
The Newcomers were a mysterious group of people from ancient times who worshipped the Cleansing Fire out of fear. They prayed to the Descry in fear of retribution.
That winter, scorched refugees emerged from the shrine, speaking only in strange tongues. They prayed to a new symbol of power, not out of love, but out of fear.
Onyx AmuletRequires Level 61+(10-16) to all AttributesModifiers to Attributes instead apply to Omniscience
+1% to all Elemental Resistances per 15 Omniscience
Penetrate 1% Elemental Resistances per 15 Omniscience
Attribute Requirements can be satisfied by (15-25)% of OmniscienceThat winter, scorched refugees emerged from the shrine,
speaking only in strange tongues. They prayed to a new
symbol of power, not out of love, but out of fear.
At the time, Innocence desperately desired godhood and sought worshipers, but found little success. When he encountered the Newcomers, he took the Descry and made it his own symbol, manipulating them into worshiping him as their savior. The Newcomers would become Innocence's first worshippers, and his first major step in his quest for godhood.
"The newcomers were terrified of fire. He used their fear to control them, to lay the seeds of unquestioning faith. He claimed only his god could protect them."
- Lycia, the Heretic
The Night LampThe Night Lamp
Urn RelicRequires Level 64The Herald of the Scourge drops an additional Forbidden Tome
No Resolve Mitigation, chance to Avoid Resolve loss or Resolve Aegis
This item is destroyed when applied to a SanctumUnmodifiable"The newcomers were terrified of fire. He used their fear to control them, to lay the
seeds of unquestioning faith. He claimed only his god could protect them." - Lycia, the HereticPlace this item on the Relic Altar at the start of each Sanctum run, flavor text
"He took the newcomers' symbol and made it his own. Finally, they flocked to him. Finally, he had the power and wealth he so desired."
- Lycia, the Heretic
The Gilded ChaliceThe Gilded Chalice
Processional RelicRequires Level 64Duplicates up to 4 random Offer Rewards upon defeating the Herald of the Scourge
Cannot recover Resolve
Cannot be used with Forbidden Tomes below level 75
This item is destroyed when applied to a SanctumUnmodifiable"He took the newcomers' symbol and made it his own. Finally, they flocked to him.
Finally, he had the power and wealth he so desired." - Lycia, the HereticPlace this item on the Relic Altar at the start of each Sanctum run, flavor text