From your post, when I was creating a content rule, I tried to find a way for the rule to test for forum object type, but I couldn't find it. Is it there such a type already?
There is a forum space type "fm:forums" and the forum type "fm:forum". You can configure the the action wizard to contain these types by adding the relevant type to the subtypes element in the "Action Wizards" config section i.e.