Got to thinking about some of the old bike lingo. This is one I remember from when I was a kid back in the '30's. It was used through the fifties, and slowly died out with the new age riders.
Yo-yo-yo-yo-yo.
Ted,
"Yo" may have died out in the 1950s where you are. But like most things, it's still alive in New York. And you'll be happy to know that it is used today by bike messengers, who are often on track bikes. Their meaning, I think, is the same as yours. i.e: heads up, watch out, I'm passing you etc.
Michael Allison
New York, NY