It may have been an escaped falconer's bird, I suppose, though it might also have pounced on someone's Christmas decorations and either made off with them or somehow got its feet entangled. I've heard of "belling the cat", but this was something new. You can just imagine the barracking it was getting from the crow...
"Oi, Rudolph, where's Farver Chrissmuss, then? Eh? Tell you what, give us a bell when you get 'ome! Oi, Tinkerbell! Twinkle Toes! Yes, you!!"
It takes a lot to embarrass a hawk.
Bells will do it, though.