When taking the car out for the day, I do a visual check of all lights (Old Semi truck driver Habit)
I don't use hand signals as most people don't understand them anyway. If I have someone right on my a$$ or if everyone in front of me is slowing down, and I feel the person behind me is not playing attention, I will turn my 4-way flashers on, for a short time, that gets people's attention (Quickly, and safety) I've had a State Patrol officer give me a "Thumbs up" for doing that. I can happily say, I have 2+million miles on my Professional License and God knows how many on personal license (52years total, got my CDL @ 18YO), with (One Accident) deemed not my fault. My $.02. Cheers Tom