Looks like a glitch. What's the user-agent for the example photo? Those chars would typically be the end of some JavaScript (or JSON), or something else that's encoded as CDATA under XHTML (and, in this case, apparently commented out, which may have been the reason it's showing up in the browser). My guess would be someone does some User-Agent sniffing, and has a little overlooked error in some code under a certain UA condition.
It might not even be PHPBuilder/(Quinstreet?)'s error/problem ... when you serve ads, sometimes you see this sort of thing coming from an ad service; you are, in effect, letting any of several hundred different companies (and their coders) put code on your site ...
