OP
advertising in the message text can be hard to spot, but what about advertising in avatars, is that acceptable?
We actually frequently allow advertising in the message - so long as it can be reasonably tied to Linux or the likes. If someone's advertising in their profile, my reaction is based on their contributions. Are they contributing and helping? I'll leave it.
It can be pretty subjective. I recently shipped a post up-stream (didn't act on it, in favor of letting an admin decide), as the post was an ad for a 'private search engine'. I didn't want to make the judgement call on that 'cause I was also particularly irritated that day.