> and yes, i think announcing it to the people around would be a good first step.
That would be an excellent way to get sued for millions for slander. Particularly if there are witnesses. And while “truth” is an absolute defense for all defamation proceedings such as slander and libel, it would be your burden to prove that this stranger was, in fact, a paedophile. I doubt he would make that easy for you to do.
> the second would be to throw trash/garbage/food at the individual (of course, if he comes after me... i may be forced to defend myself :)
That would be an excellent way to be arrested and charged with Assault, and possibly Disorderly Conduct. If the paedophile attacked you for throwing stuff at him, he may be able to plead “Self Defense”. Then it would be your ass in the sling, not his.
On the assumption that you believe this bulletin, your best thing to do if you see those symbols is to keep your kids away from that guy.
so... best to wait until there are no witnesses. check
Loudly ask them if they know what it symbolizes. After they tell you they don't know, loudly tell them. Anyone who's innocent will appreciate the warning & perps will know that people are on to them, making it more difficult to connect with others, the purpose of the symbols.