There is a simple thing to do "post as if you aren't wearing any signature ad and you will be safe". I think this is a simple thing to understand & apply, or maybe I am wrong.
If you posted as if you weren't wearing a signature and you posted a short one liner it would be looked upon as spam unfortunately, but if you don't, it wouldn't be thought as so. I'd usually just pm the op if I'm going to be posting something short. So it's not upon as spam and the point still gets Across