to let you know who link you thread

[Marco van Herwaarden]

Well since you don't have access to all possible other websites, there is no way of knowing who and where linked to you.

The closest you could ever get is somehow do a search for your link in search engines like google, etc.. Not something i would like to do.

Another approach, but also far from perfect, would be to use referrer for that, but this is also not 100%. You could get a lot of false positive or false negative information.