I'm a huge fan on the "DO NOT PET" tag. I've started turning into a game.. People see the bright red tag.. I said "there's a good chance he'll bite your fingers if you reach for him"... Then they still do it, and I let out a BIG OLD laugh while I pull Helo back from chomping.
Yeah I'm finding most people respect it... they assume he's a service dog or a recently rescued/scared dog. I just let them believe whatever they want if it means they stay away!