and from what I can tell, they are not approved by USCG.
As others mentioned -- not sure if people would recognize them as distress signals.
Boat US Foundation did some tests a while ago using various distress signals -- the results were not very encouraging.
I reckon aerial flares should go "BANG" like a firework. Nothing gets attention like a loud noise. If you hear the bang and look around you might just see the flare.
I was down below in the middle of the English Channel one time and heard/felt this enormous thud! I ran on deck to check the rigging and the other guy on board just laughed.
"Look at your watch," he said.
"So what?"
"It's just after eleven a.m. Concorde from Paris to New York."