In this forum you can post texts that exist within the world. Examples of these include

Character Journals

Self-explanatory, a journal written and updated by your own character regarding various events and thoughts that come up by time.

Books

Well, more like chapter(s) of books. I don't expect anyone to write an entire book here. The books can be about absolutely anything you think that anyone would've written about in the world.

Research notes

Things your character encounters and finds worth jotting down. Or perhaps something an NPC has done research on in the past and you feel it's worth writing down for sake of referance.

Tales and stories

Not necessarily written down, but can also go by spoken knowledge. Folklore, warstories, things you heard in a bar in some corner of The City last week, anything.

Songs and poems

Same as with Tales and stories, there aren't necessarily existing written down in the world, but exist as spoken (or sung) legacy in the world. Fun things you may come up.

Anything else

Flyers. Newspapers. Anything. The above list is by no means exclusive. If you feel there's something along the lines of these that you wish to share, post it here. They don't have to be in anyway remarkable to the storylines, just something fun to think about and write and maybe further help expanding your character.

Note that these texts don't by any means have to be written (or even known) by your character. You can use an imaginary NPC that has written a book, concluded a research or composed a song. You can also use an unknown artist. Just as long as you don't take control of other peoples' characters as the author or well-known NPCs