I thought about this on the way home from work last night, riding in commuter traffic on a pretty busy road downtown (Cleveland). When I am forced to ride a little closer to parked cars than I really care to because I’m afraid of getting doored, (somebody opening their car door in front of me) I found that I started looking into the mirrors of the parked cars. Most vehicles, with the side view mirror adjusted correctly will let you as a bicyclist see into a vehicle to see if there is a driver. If the vehicle looks empty, I know I’m fairly safe. If I see a person behind the wheel, I take precautions, try to catch their eye and prepare for a door opening or the vehicle to start moving. I never assume I’ve been seen.
I also found that when signaling drivers of my presence, I need to be rather overt. I save my wimpy bell for the bike trail. I’ll outright holler to get attention, waving my hand over my head if I need to.

Eyes All Around.