There's a conflicting opinion from a cop on Reddit. Basically he agrees that you should shut your mouth, not let them search your car just for the heck of it, etc ..., but when it comes to the question "Do you know why I stopped you?", playing dumb won't do you any favors. There's a lot of other useful info he says that are relevant to the thread.

http://www.reddit.com/r/everymanshouldknow/comments/1rsizj/e...

Yes = admission of guilt

No = admission of negligence

The only right answer is a non-answer: "Hold on, lemme get my license and registration."

Please. Then they charge you with uncooperative. You guys are assume all police officers are bad. I have seen officers asked and let people go after giving warning.

Let's be clever here, don't be dumb. The right thing to do is to turn on your cellphone's camera and start recording.

No they aren't. They wouldn't pull you over if they lacked evidence. Are you seriously suggesting saying nothing even if it is abundantly clear what happened? If you admit it and explain why you did it(maybe it was just a stupid mistake) you have a chance of not getting a ticket. Only time in my life I was pulled over and I explained what happened and why I made the mistake. Got off with a warning.