I started a tag a while ago called spelling_with_anus for when the anus is used to represent a 0 or an O, which typically appears in conjunction with writing_on_butt. I'm 99% confident that there is not a preexisting tag for this.
Examples:
post #3681559 post #3947038
Unfortunately, I think this tag may be too vague and also too specific. "Spelling" conventionally excludes numbers, and the tag could presumably be expanded to include similar uses for vaginas, breasts/pecs, and even penises for 1s. Perhaps "anatomy_as_symbol" would be the best solution? Or perhaps this should just be a set instead of a tag.