I had an accident two months ago where something similar happened:

I was waiting on my bike for an opening at a roundabout (rotary for US?) and the car behind me who saw me (he later confirmed it) started looking for a good timing to drive into the roundabout too and forgot about me.

He then started accelerating to drive into the roundabout just behind another car while I was still right in front of him. He completely destroyed my bike (which fell under me so I could walk aside and be safe) without noticing anything.

So.. yeah, the "see bike, say bike" rule seem nice and not a big deal. Please consider trying it :)