@eranzelnik It certainly does make a difference. Did your neighbors get one? I'd talk to the police on the non-emergency line; this sort of shit is troubling.
@eranzelnik Keep it, keep the envelope. Report it to your local USPS. Not saying they can do anything but it's clearly hate speech which may get their attention. At the very least, they have a record of it in the event more of these things are reported.