I am sure most of you are aware of this by now, but I didn't see any posts and thought I would make it readily available.
http://mgaleg.maryland.gov/2013RS/bills/hb/hb0577f.pdf
"FOR the purpose of providing, for a vehicle required to display two registration plates, that the front registration plate may be stored in a certain manner inside the vehicle if the vehicle was manufactured without a means to secure and display a front plate; making stylistic changes; and generally relating to vehicle registration plates."
You can only run without a plate if there is no way to mount to the vehicle.