Funny timing... Yesterday I installed one of Jac Vinson's turn signal beeper kits on my 650. It has a very loud beeper that was originally selected because it was mounted down below the fairing. But he sent me a new easier install procedure to try out. With this procedure it mounts right under the handlebar cover.
In the new location it is LOUD! It is almost embarrassing to leave the signals on when stopped in traffic at a light waiting to turn. But I saw driver's looking around. It sound's like a huge truck is getting ready to back over them... (A lot of trucks have the backup beeper - sounds the same.) Even when moving at surburban cruising speeds, I think it is loud enough for driver's to hear when I turn on my signal for a lane change.
From a safety standpoint, it is not a bad thing. But I think I'm going to try to muffle it a little - I'm too shy to be making all that racket.
Jac is experimenting with other beepers that put out less sound for the new mount location. But in a way, the current beeper mounted high (under the handlebar cover) does what Mary is looking for - makes loud noise without sounding like a horn. Even going straight, just hit the hazard flasher switch, and you're making a racket...