imported post
Under Md state law there is no prohibition against OC if you have a MD PTCF. However, many of the urban counties and MOST of the urban cities have ordinances prohibiting the "display of a firearm" in any form, so you need to know your local laws.
HOWEVER, all that said, you need to remember that EVEN if you do have one of the incredibly rare and elusive MD PTCF, if a LEO (particularly a MD State Patrol officer) sees you OCing, you WILL be stopped, disarmed, proned, and probably arrested. And even if it's found that you were legally doing so under the letter of the law, you will most likely have to sue the state to get your firearm back, and will probably have your PTCF revoked for being a rabble rouser, and not being of "good character"...
Get a lawyer if you REALLY want to be a test case, that's my suggestion...