What it looks like is the first and last post have the big ones under a username, except if you have a personal title. Also the ones along the bottom of the post are on the last post too. I think!
The ads also change on every page view so they will not appear the same everytime. Also from a personal view, I don't think it looks like you are endorsing anything at all, just because it is under your name.
PS, don't get them if you are a mod either!