So does Stack Overflow, although they tell you very clearly that your user ID is embedded in the link, right in the "share" box (and it's not obfuscated in any

So does Stack Overflow, although they tell you very clearly that your user ID is embedded in the link, right in the "share" box (and it's not obfuscated in any way). SO goes so far as to give you little notifications and achievements whenever a certain number of unique visitors follow one of your shared links.