some weird signature? problem (don't know what else to call it)

Have you installed any suspicious program the days before you noticed this the first time? Or maybe you installed "Free Youtube Downloader"? :D

First, look at the addons of your browser, maybe there's something suspicious.

Second (if first doesn't help) install CCleaner and run a scan in the registry. Delete all of them and then check if the "problem" shows up again. If yes, run regedit.exe and search for suspicious folder in Local Machine - Software and Current User - Software. Maybe there's a folder which is called "cnet" or "Free Youtube Downloader", don't know. If you don't have any programs from cnet installed, than you can delete the entry in the registry and then check up again.

Also try to reinstall your browser, maybe this can help too, don't know :)