That's the first I've heard of that. Everything I've read the last 37+ yrs of driving has been you flash your high beams to pass. This is also in the motorcycle handbooks, H-D owners manual and every car manual I've had.
Flashing to tell someone it's OK to turn in front of you is counter to all those:newsmile055:.
You must have missed my first statement - this is a standard courtesy signal everywhere I have lived in the US that means you're yielding to someone else and giving them permission to go ahead.