How often have you gone to pass a van parked in a line of kerbside cars, and it seems to be signaling to pull out. You lower your approach speed, potentially slowing following traffic.
Only when you get closer can you see the left indicator's flashing too: it's on delivery, with its hazard lights on.
Perhaps the driver shouldn't use those warning lights if he's taking his place in a line, and not especially causing an obstruction in his own right. But, it seems to me, it would be very easy to make hazard lights distinguishable from turning signals.
Configure them to give a brief double-pulse of light, then the usual pause before another double pulse.
Seeing only one side of the vehicle would then be enough to let you know the driver's immediate intentions.