The last 100 yards or so of my commute is through a bus depot and up the sidewalk towards our office's parking garage.
I'm usually saying "on your left" until I'm blue in the face and creeping along at their walking pace. Pedestrians are far less predictable than cars, they tend to "drift" on their walking path, they wander around without a glance.
But if you are on the sidewalk, you really should be going at their walking pace, shouldn't you? Is sidewalk cycling legal where you live?

It isn't where I live, except in residential areas (a law that was enacted so that kids don't have to ride on the street while they are still learning), and when I am walking downtown, it really irritates me to hear, "On your left!" like I am supposed to move over for a bike. It irritates me even more when they don't even bother with that, of course, but really, if you HAVE to be on the sidewalk where you aren't supposed to be, you should be ceding the right of way to pedestrians.