Currently there are two posts tagged with 18+_adults_only_sign,
but tag category is character.

1) post #2824429 has sign-version (so 18+_adults_only_sign should be general category?)

while
2) post #1148239 has apparently anthropomorphized the 18+_adults_only_sign.

Switch 18+_adults_only_sign to general category?
and add another character tag to post 1148239? (living_18+_adults_only_sign ???)

The first one looks like a "no 18" sign more than a "18+ only" sign. But either way, 18+_adults_only_sign seems like a very clunky tag name. "18+ adults only" is a little redundant since 18+ already implies the age group without "adults only". But also the + in the tag name feels like it could be a problem in some situations. Maybe adults_only_sign or 18plus_sign or something.

For the second, maybe the generic animate_object+whatever_sign would be best. I don't think it should be a character tag unless it's specifically someone's character, then it should be tagged whatever they named the character.