This happened to me quite a few times whilst flying a police helicopter. I used to respond with the nightsun, on tight focus. As in "call that a torch?.....THAT'S a torch!" They usually got the message, but seeing as we could easily identify the address, a couple of them were prosecuted as well.
A more recent one near an international airport was reported to ATC as it was a prevalent problem and we had been specifically requested to do so. I was subsequently required to make a statement to the police, who told me they were treating the local incidents very seriously, as potential terrorists attacks.