That would depend on the song you are singing I guess. No one would look twice at some hippie skipping down the street here singing Sugar Magnolia (It's a Jerry kind of town), but if you were out singing Metallica's Master of Puppets or Ride the Lighting, perhaps people might pause.
The only hotel that faces Union Square is the Westin St. Francis, which is very nice. Very nice. Really, very nice. Nice enough that when Queen Elizebeth arrived here a day early because of high seas and they didn't want to take her Royal Yatch Britannia up from Santa Barbra that's where she stayed, and for the second time, I think she was there on the way to her honeymoon at Yosemite also.
As a bonus they do have a Victoria's Secret in the hotel.
But of course I'll wash your back, water conservation and all.
