Hot off the Press! These are not your eldritch manuals or ancient folios of doom. These are random books, a GM can use whenever a PC reaches for a shelf, which usually happens when said GM is least expecting it. These can be found in most libraries, many private homes, and anywhere else one could expect to find a book. More than a few have some built-in plot hooklings as well, while others, like many books of our age, are plain drivel.
Common for sailors to get lashings for punishment. Sailors would then get tattoos of god symbols on thier back so the thrasher was less likely to whip the symbol of the god.
Others say symbols bring bad luck. They draw the attention of the god and it could be wrathful.