Hand Signals

We've got the wave. It's friendly, it says 'hello', 'nice to see you', that sort of thing. We have a lot of gestures for all sorts of unpleasant things (I probably don't need to list them here).

But what about when you pull to a stop and get distracted, fishing for something you dropped a block back, checking to see if you have cash in your wallet, or whatever, and then notice that somebody is now behind you, waiting for you to get going? Why don't we have a universal hand gesture that says 'oh, sorry about that'? Some way to let people know you weren't being intentionally rude while you get out of the way?

Maybe there is one and I just haven't heard. (I'm often the last to know about these things.)

Any ideas?