After refreshing ads few times on links in my sig I saw this: 1118583844-216.9.35.51-us82jsdd|400|900|4|1|MSIE-Firefox-Safari-Netscape-Opera Wasnt shown as a link, but as normal text. Sticks out like a sore thumb.
That's not an ad, that's the ad network preferences (first line of the cache file). But if you see it in an ad, something is not be right. Your cache file might be corrupt or something. Are you using the default PHP setup or something else?
Default PHP set up as far as i know, Ill get a new set up file and over write the old one, gonna see if that helps. edit: that seemed to fix it.