My MUP overtaking method: 1) Go slow. 2) Ring bell twice from a good, non-startling distance. 3) Call out a greeting like "Good morning" in a cheery, friendly but loud voice, followed by "I'm passing on your left." 4) Say thank you.
I like the bell because it's kind of friendly, compared to a horn or a shout, and it's bike-specific, so the pedestrian knows there's a bicycle coming. The bell and the greeting are really just to make sure you have the walker's (or slower rider's) attention before you tell them where you're passing. A simple "On your left" is interpreted as a request to move left about half the time, it seems.
The MUPs in my suburb are uncrowded, so they work well for riders and walkers.