Every time you visit a web page your browser sends a HTTP request and with it, a small chunk of information about your system. This is normal and nothing to be concerned about, this signature you're talking about sounds very much like an autogenerated image I've seen plenty of times before. It's not someone taking the piss out of you, the image changes so everyone who looks at it, it shows them their own info.
Spoofing HTTP headers is easy but your IP, not so easy. You could use an anonymous proxy or something like Tor but there isn't a reason to panic. As I said, the same goes for everybody and as long as you don't run any vulnerable services on your PC you don't have anything to worry about.
Have a look
here, it'll give you some helpful information and you can see exactly what you computer has to say about you
