Tags and which ppc they are comming from

Hi

I have noticed that people are using tags at the end of there url like this ?ref=7s this is to know where the traffic is coming from.

Now ?ref=7s is coming from 7 search and is networks , that much i know or ?ref=ma is coming from mamma and its networks , but where and what is this from ?ref=mv witch search engine is mv

here are more

?ref=bgo
?ref=ouk
?ref=fw
?ref=espot


thanks

Miva, an english ppc company