Sign, Sign everywhere a sign...

We have gestures for almost every type of problem you're likely to face when driving a car. Someone waiting to pull out of a drive in front of you? Wave them out.
Someone just let you in? Wave graciously to say thanks
See someone with their lights off? Flash yours
See a cop lying in wait? Flash your lights at other motorists to let them know
See someone with their turn signal on? Put yours on or turn on your hazard flashers or alternatively open and close your hand and they'll usually figure it out.
Someone cuts you off? Well, you all know that one right?

The only one we don't have a gesture for is to apologize to a fellow road user for something stupid we did...and stupid is often the cause of road rage incidents. Lets say you don't see someone in your blind spot and you change lanes and nearly force them off the road. They're angry and they come screaming up beside you intent on giving you a piece of their mind. What do you do? Scream back or flip them off? Surely not, it was your fault after all. And yet, if you do nothing they're likely to assume you're ignoring them, or don't care, which is only likely to compound the error.

I submit a great idea is to carry a piece of white cardboard in your car with the word "SORRY" written on it in large black marker and keep it accessible. If you do the inevitable and screw up, instead of making matters worse by ignoring the guy, or gesturing in a way that may be mistaken for something else, hold up your sign and smile. I'd be willing to bet a load of money that one simple move would eliminate a slew of road rage incidents across the country every day.

PS: If some enterprising soul reading this decides to market them and sell them at gas stations etc, be nice, give me a cut.