A childhood belief about road signs

I would always see the signs on the road that read "Grooved Shoulders" and had a picture of a man on a motorcycle. Knowing that groove, was like to dance, I thought you had to rock to the beat with your shoulders, but you had to be cool, like motorcycle dudes! I always thought that people with cameras hid behind the bushes near the sign and would videotape the people dancing and get a kick out of it, and show it on TV. I would always start dancing when we came to these signs, even if there was no music on in the car. When I saw nobody else in the car was doing it, i thought we would get arrested for not following the sign. I would sometimes start crying and my parents had no idea why. I still don't know what that sign means, but its not what I thought!!