At EuroBillTracker the Euro bills are tracked around the World by registering their series number (which are printed in the bills themselves).
Whenever a bill is registered by two different users a "hit" occurs. It is by collecting and monitoring all the bill hit that their movement are tracked. Besides simple hits, each bill can be registered more times in multiple hits.
I have registered my account in 2006. In the first years I have obtained a couple of hits, but then I decreased my registering activity, but, lately, I have restarted to register bills again. You can check my profile here: EuroBillTracker:completo.

In the following pictures are shown the locations of all the registerd Euro bills around the World (as in 13/01/2019) and some examples of hits.