On Your Left

Ok, so one of my pet peeves when I'm running is a biker who doesn't sufficiently let you know he's coming and going to pass you. You're supposed to say "on your left" (but not when you're right next to the person) or ring a bell or something. That being said, I ran into quite the predicament today during my speed work run...I actually passed two people on bikes! They were a father and son (I presume) on a nice easy bike ride on the BWI Trail (bike path by the airport). I wasn't sure if I should say something or not. If I could... I didn't have the breath/energy too. I guess I'll just count on them hearing my breathing and/or footsteps. That was an interesting first :)