They are ceiling or wall mount brackets for mounting up high for PA use .. IMHO.
I don't think you'll get any argument on that AB.

The underlying theme here is that something doesn't jive in this fella's auction, maybe.

It's hard to tell from the pic if the color is accurate for Heath, but the brackets do seem to match the horns in color, and it seems like it would be going to a LOT of trouble to source repro Heath decals.

After reviewing the pics closely, i believe these are NOS, and i believe the brackets belong with and have always been with those horns, the color matches perfectly, and they're in immaculate condition.

I can only conclude by a wild ass guess that Heath must have offered the 511A w/bracket as a PA speaker for at least a period of time. I knew they made a few mixer amplifiers, and column speakers, but was never really aware that they offered anything for distributed sound.