Just curious if anyone has ever been stopped or asked for their credentials.

FCC or FAA number?

How stupid do I feel !!!!  Yes FAA  number.

no. never been asked for it.

Yes, I have been stopped in a county Metro Park.  I found out that there is rule against it that I was unaware of.  He gave me a print out of the regulation stating :
"25.1 Prohibited
No engine-powered, radio-controlled, self-propelled, free sailing miniature model and toy airplanes, boats, cars, rockets, sirens or other noisemaking devices are permitted to be started, operated, flown or used within the confines of the park, without a permit."

I honestly think the officer knew what he was looking for though.  He asked If I had "one of those registration number things".  I asked if he meant the FAA registration and he said "Yea, that's it".  I showed him the one I carry on me and then (once I landed the Spark) showed him the one that was on my drone.  He glanced at it and gave it back.  He didn't check my ID vs the registration, call anything in, verify online... I believe that he was just seeing if I had one.  So, so far my experience with law enforcement as far as the FAA has been negative.  I have been asked when I contacted the airport nearby and they were a lot more thorough and courteous with me.