What can be done about fake monks? in the city where i live (Toronto, although this is an issue in many cities around the world), there are people dressed as monks soliciting others on the street for donations. In return, various good luck charms are offered.

The fake monks speak little English, and will try to justify their begging with the claim that donations are for building a temple back home.

Is there anything I can or should do about this?

Are these fake monks giving Buddhism a bad name, or at least obscuring Buddhism's true message?

Are the fake monks doing an ironic good by giving people the chance to practice generosity?
I have some suggestions. 

Guard yourself against any possibility of Wrong Speech by not saying anything about these persons, their motives, or actions that you don't personally know to be true; even if it seems extremely likely that they are being deceptive. If you want to warn family &amp; friends, stick only with what you know to be true such as "In the tradition I study, monastic rules don't allow monks to ask for money or sell good luck charms."

Guard yourself against the arising or continuing of any negative states by not identifying with this issue. This is not personal. Cities have always been magnets for people inclined to do "creative fund raising". ;-) City dwellers are pretty savvy about this type of thing and it's unlikely the media will downplay it indefinitely. It's too quirky of a story for them to ignore forever. 

Guard yourself against the attachment of "me and my" Buddhism getting a bad name. Truly awful things have happened in the contexts of other religions; bloody wars, sexual exploitation, financial scandal. 

The teachings of the Buddha shine on. A little thing like this can't tarnish it. :)