I have an Incredibell Brass Duet, which naturally does two dings with one push of the thumbie, once on the press and once on the release. I find that it works really well if I press while a ways back, then release when reasonably close. People's brains are very good at inferring speed and distance when given a couple of reference points for the sound, so two dings separated by a half a second or so actually provides much more information to the ped than a single ding does.

Ironically enough, I was on the MUP this morning towing a Weehoo trailer, which makes my rig about twelve feet long in total, and rang my bell while passing a cyclist, who then proceeded to swerve right into me and almost take me out. She then started yelling at me about how I "need to say something" before I pass. Believe she was wearing earbuds.

No matter how polite you are, some dimwit is going to decide you're a jerk.