In the US, only large trucks will have a back up horn. You know the one. The BEEP BEEP BEEP of the garbage truck at 5am.
In India, pretty much everything with four wheels will have a back up signal. Not the typical BEEP BEEP BEEP you might expect. Instead you'll here something with more of a melody, such as The Wedding March, Pomp and Circumstance, and a wide variety of Christmas carols. From the Popular music front, Celine Dion's "My Heart Will Go On" is a common tune. I even heard J-Lo's "On The Floor" the other day.
I find it insanely entertaining, although somewhat annoying, depending on the driver's taste in music.