I always say, "Passing on your left," and I do sound authoritative, but it just kind of comes out that way. When passing, I always say "thank you" and sometimes add a "good morning" and smile.

My hubby doesn't say anything and I've watched people jump, seen him almost take out a jogger who decided to cross in front of him without looking, etc. I just holler from behind him that we're passing on the left. I guess I need to lead.