Let people know it was "My Bad"

OK - here is the simple question... When someone cuts you off in your car we all know the multitude of non-verbal communication we can choose from to clearly illustrate our frustration. But... what about the time when you realize you are at fault? Should not there be a universal non-verbal sign for "my bad?"

I had this happen the other day when I completely spaced and started to turn right on red when there was a car coming from the left. I was certainly in the wrong and I wished there was someway I could have indicated that. All I wanted to illustrate was "Whoops, sorry - that was totally my bad." I think I pointed at my head (to show that it was empty) but I doubt my message got across.

If you wave you look like a total ass "Thanks for letting me almost kill you!" same is true for a smile and a shrug clearly sends the message "So what, human life is cheap."

So - what should it be? A hand gesture - maybe a fist to the forehead? (I'd punch me I were you) or what?

Lastly, I know it's not Tuesday... my bad.