I’d guess that you’d have less than 50% of drivers that know what the hand signal for stopping means. Unless you are a cyclist, you learn it for your permit and never think about it again. The left signal is pretty self explanatory, but the right turn would probably stump a lot of drivers as well. Even cyclists mess that one up. I’ve seen several times where they’ll use their right hand to indicate they’re turning right.
You're probably right for some reason they stuck with me through out the years.