That's why, years ago, I started building actual lighted turn and brake signals into my bikes, eventually going to DOT-rated units with as large a surface area as I could fit because it's easier for people to see those.
My quest really started when a *police officer* waved at me while I was signalling, then I turned and they seemed to figure it out then.... I realized if *they* didn't know what I was doing, I couldn't expect anyone else to, so I started using the same "language" all the other things on the road use, since even if people don't always *use* them, they still know what they *mean*.