You can't win with walkists. I have bells on 3 of my 4 bikes. I try to use them first at a distance, so as not to appear "aggressive", then I use them again as I close in if they haven't reacted, and again if still ignored. I'll only resort to a call-out if they are still ignoring me, by which time there is not way they are reacting anything other than surprised and annoyed (usually they're on a call or listening to music).
If you DON'T ping them then you get "where's your bell?". My bell-less bike has a very loud freehub which I use with some success to alert walkists and, in fact, never generates any negative reaction.
The bells I do have are cheap ones - whatever I can find that is small, the right colour and has a moveable pinger (ie you can move where it sits around the circumference of the bell to help nestle it up against other controls on the bar and be reachable from the grip).
Someone earlier mention the Spurcycle bell and also the Rock Brothers copy. I was all set to pick up a cheap copy, then I read an article about the designers of the original and how they have essentially (through naïvity mostly) been ripped off by having their design copied and mass-manufactured. This doesn't sit well with me, so I didn't order one. That said, I didn't put my money where my mouth is and order an original either.