First off no, not all police officers in the United States have radars in their law enforcement vehicles. There are different methods for the police to determine or calculate your rate of speed such as clocking, using radar, laser and vascar. The Virginia police officer should have told you what method was used or it should say on the citation.
While many people may request to see the radar that took the speed reading it is not required in most jurisdictions that the officer show you the radar equipment. However you were found to be going 12 mph over the speed limit, if you do not agree with the ticket you can choose to fight it.
It is possible the radar, or other speed measuring device, was being operated improperly. Or it could be that the officer mistook your car for another, or he made some other mistake. If you believe this to be the case and that you were not speeding then you can plead not guilty and go to court. The burden will be on you to prove the likelihood of that mistake or to show that the police officer was mistaken about your rate of speed.
So it is a personal choice to make if you want to plead guilty and pay the traffic ticket or plead not guilty and go to court over the citation. If you want to go to court you can hire a lawyer to help you or represent yourself. If you choose to represent yourself, you can get help from places such as the National Motorists Association. The NMA has data on state speeding laws, common radar errors and other information that you may want to read up on if you choose to fight your ticket.
If you are convicted of the speeding citation since both Maryland and Virginia are members of the Drivers License Compact (DLC) the VA courts will inform the MD MVA about your speeding ticket conviction.
The Maryland driver's manual currently states that once the MVA receives ticket information from another state they treat it as if the violation occurred in state. The MD Motor Vehicle Administration site notes that if you are convicted of a vehicle-related offense in a jurisdiction outside of Maryland, the MVA may assess points.
There may also be more repercussions for you as a MD provisional license holder. The MVA notes that convictions or "Probation Before Judgement" (PBJ) for moving violations while holding a provisional license will require the completion of driver improvement program and/or suspension/ revocation of your driver's license.
To get a full MD driver's license drivers must hold a provisional license for a minimum of 18 months and be conviction free during that period. Convictions thus restart the 18-month minimum waiting period.
Finally the out of state ticket could also affect your insurance rates since it would likely be placed on your Maryland driving record where your insurance company would see it the next time they pulled your motor vehicle record (MVR). Whether it would raise your rates would depend upon your insurance carrier's rating system which you could get information on from your insurance agent or the MD Insurance Administration, the insurance regulator for the state.