MD does NOT recognize any cc permit other than their own hard to get one.
You can cite FOPA but only if the gun is unloaded, locked in the trunk or equivalent, and with no ammunition near or in the same container.
General advice: Do not have any gun, ammunition or gun accessories in view in the car. In one case in MD, an officer stopped a PA car for speeding (85 in a 55 zone), spotted a speed loader in the dashboard shelf, and searched the car, finding a gun in the console. The judge ruled that the speed loader was probable cause to assume a crime was in progress. The guy was convicted, but I forget the full outcome.
Drive reasonably and with traffic. Don't stand out or drive in such a way as to practically beg the cops to stop you. Don't display "cold dead hands" or "off the pigs" bumper stickers. If you want to be inconspicuous, don't drive a flame red Ferrari or a beat up VW bus with marijuana plants painted on it.
In other words, act sensibly and the odds are that you will never have a problem.
Jim