I have a horn that toggles through different sounds of a car alarm when you keep it on long enough. If a car blocks my passage I put it into operation for as long as the car keeps blocking me. Of course, I pay attention to whether the car has a safe way to move out of my way and/or whether the driver acknowledges my presence and tries to do something - I activate the horn only when there appears no other way out. It is a wonderful negotiating instrument, nearly failproof
- I do not need to yeel, gesture - I just press the button.
I just scowl. But, I'm not sure how much it helps.
It is only rarely that a car will block my forward progress along streetside bike paths, usually when I'm pulling a trailer.
And, only one intersection on a median strip bike path where cars regularly park in the middle of the bike path waiting for lights and hole in traffic. They mostly leave the vehicle intersection clear, but pack in front of the median strip bike path... they are just bikes and pedestrians trying to safely cross after all.