THIS is exactly why I notify the officer I have a gun. Imagine getting pulled over in Maryland, and having the officer notice a gun he wasn't notified about. You will be looking at the wrong end of his until he calls backup and ascertains that you are not a threat. It is so much easier to let him know it's there to begin with. As I said before, my experiences with MD LEO while I was legally carrying have been very dull. I see notification being as much for my own safety as for the officers.
This!!!! ^^^
If I was able to carry in MD, I'd much prefer to notify the officer than be unlucky enough to print and then turn a uneventful situation in to a "GUN!!!!" hassle with a firearm pointed at me. I'm not a fan of having firearms pointed at me, and assuming that the cop is a professional (and I'd like to assume that 99% are) I don't care if they know that I'm legally carrying a weapon. I would refuse a search of the car without PC and/or warrant, regardless, but for my comfort, it's not a big deal.
Similar thought- If you're in a interrogation room with your attorney, and being questioned about a crime you didn't commit, and you have great, and documented aliby (you were in Paris for the weekend with stamped passports etc.) Your lawyer would likely encourage you to provide that information to eliminate you additional hassle- would you keep that to yourself, only to require additional scrutiny?