This law clearly would not be enforceable in the the US (you can’t start trying to enforce a trademark that you haven’t been defending and that is in wide use).

Having said that, there is recent precedent where FB differentially enforces foreign laws, apparently for their own political/financial reasons.

For example, Palestinian political speech about Israeal is subject to much harsher censorship rules than Israeli speech about Palestine.

So, this case really boils down to how much FB values its political/financial ties to the city of Sarajevo.