I believe that since you want to run a business, then yes you need a permit. As a homeowner doing work yourself, NO! As for DirecTV, Comcast, etc, Since Cable TV doesnt really use voltage, then no you would not need a license to install it! Also, most likely, those type of companies probably operate under an agreement with the state that as long as they, or a contractor they sub to has a state license as a general contractor, then they are covered. As for the alarm comment, also the same thing. If you are a homeowner then NO, but a business, then YES! The is what I was told when I did my entire home with ethernet, cable, etc. This is what the permit office in Prince William County VA told me. This of course was 5+ years ago, so something may have changed.
Here is what Montgomery County has to say. Read towards the bottom.
http://permittingservices.montgomerycounty...ing/bc/nfmp.asp
DO I NEED A SEPARATE ELECTRICAL PERMIT?
An electrical permit for mechanical equipment and appliance installation is required when new high voltage branch circuit conductors or feeder circuit conductors are installed. An electrical permit is not required to hook-up appliances to existing conductors and to add/replace disconnect switches.
Electrical permits will not be required for low voltage control wiring except when such circuits penetrate fire-rated assemblies, or are installed in an air plenums; provided the voltage does not exceed 30 volts.
Frederick County
http://frederickcountymd.gov/FAQ.aspx?QID=458
Any new wiring, including low voltage, service work, reintroduction of service, generators, pools/hot tubs, street lighting and illuminated signs require an electrical permit. Replacement of an appliance or a fixture not of the same rating requires an electrical permit.
Charles and Howard county websites appear to be broken. So it looks like a mixed bag!