It's legally mandated in my city so I guess the polite thing to do is ring a bell, you know, just stick to the protocol, for everyone's sake. A bell however seems at least as likely to startle someone into behaving erratically as not.

As far as the pedestrian's safety is concerned what matters is either giving them a wide berth or slowing right down when passing.

Whether on a bike or not I'm sick of all the modern world's beeping and ringing and buzzing and blaring and if I'm wearing noise cancelling headphones that means I don't want to hear it. Don't tell you're being annoying for my own good because you aren't.