The thing is, if they stop and wait for you it's hard to be sure it's YOU they are waiting for. It could be a cat in the road or something. It's best to get eye-contact and return a smile and wave or something like that just to make sure. You can have trouble whether you try to pass someone on the left or the right. I always try to make sure people in front of me stay there until I'm certain it's ok to pass them.