Blackwoe Handbook of Applied Religious Iconography

This supplement for Pathfinder 1st edition delves into holy symbols and their interaction with magic, monsters, and player characters. It contains both crunchy rules and extensive discussion, much of it (because I get carried away) in a broad parody of academic style complete with extensive references, both real and fictitious. But even if you're not interested in reading all that - and that's fair enough - it's full of rules and ideas you can apply in your games.

Includes:

Three new symbol-focused archetypes! The icon idolater warpriest places trust in a deity's symbols, not mere arms and armour, channeling divine power through them in searing bolts. The iconographer occultist draws on the power of sacred symbols for an echo of divine power. The audacious petitioner rogue is bedecked with holy symbols, bargaining with any gods who will listen for the aid she needs. 

Twelve new holy symbol-related spells! 

More than 50 new feats for symbols and associated actions, including one for every canonical domain! Even the humblest, least theologically-inclined peasant can make use of Deference feats to gain minor benefits from the holy symbols of a deity they trust.

Nine pathetic little monsters to pester your NPCs, all of them vulnerable to holy symbols (similar to real-life folklore that monsters fear religious symbols and other sacred items)! Menace townsfolk with gutterspites, and harass farmers with malevolent ditchdrakes!

New traits and drawbacks related to holy symbols!

Variant holy symbols, symbol-related items, garlic flowers, and other items useful for holding unpleasant beasties at bay.

A comprehensive summary of existing rules relating to holy symbols.

Suggested clarifications of those rules, plus what it means to "worship" a deity, losing a deity's favour, and the importance of alignment vis-a-vis one's deity of choice.

New rules for symbol-like anathemas, like the traditional cockatrice hatred for roosters and a genie's dislike of iron.

Plus essays of various length on...

‘Stay Back, You Fiend!’: On the Holy Symbol as Anathema

Holy Symbols (and How They Get That Way)

An Acquired Taste: Garlic and the Undead

Faith Without Focus: the Curious Necessity of Divine Symbols in Clerical Spellcasting

...all with suggested in-game applications even if you aren't interested in reading them!