I don't gesture or do anything that might lessen my control of the bike. I assume that all cars behind me are just as likely to kill me as not. The rabbit and Whoooosh in Watership Down is a good analogy. I take the blue line. I use my mirror to make an initial determination about traffic behind me, and then if it looks safe to do so, I turn my head and make absolutely certain nothing is coming. If necessary, I stop and wait for a gap, then cross at close to 90°. An aggressive naked man with a knife is at a disadvantage when going up against an armed medieval knight in armor. The more aggressive he is, the greater his disadvantage. The less aggressive, the greater his advantage.

In the particular case raised by the OP, when near an intersection I examine every passing car for a turn signal. It's always possible someone will turn while abeam of me without signaling. I have had to go around the corner with the car, but I'm prepared to do that. Drivers more frequently than not make the mistake of seeing a bicycle and thinking "5 mph," when said bike is really doing 15-20.

Anyway, I try to never assume some level of competence or visual acuity on the part of a driver.

Thus I only take the lane when the difference in speed between me and traffic is maybe 20 mph or less. A riding buddy who was big on taking the lane is now recovering from a concussion after a car brushed him while riding alone on a rural road. He was very lucky.