Pedestrians have the right of way here. Unless i have a lot of room i don't tell them passing on the left anymore because a lot of them just move to the left when you say that. (My stepfather got hit by a bike doing that very thing, no one was hurt lucky lucky)

I say HELLO! or Excuse me! and they turn, look, and move.. (this is not on a bike trail)
on the bike trail i am more apt to say "on your left" because people there are expecting bikes..