I do monitor marine radio channels while mobile as a member of the USCG Auxiliary and don’t hear too much abuse of Marine Radios in the Baltimore/Central Maryland area. Don’t scan all VHF-FM marine channels only the CG, Distress channel 16 (156.800 Mhz), Channel 12 (156.600 Mhz) alt CG channel for my sector, and channel 13 (156.650 Mhz) Navigational. The CG is able to use channels 21A, 23A, 81A, and 83A for their operations and these rotate at each to minimize interference amongst units. The Sectors/Station only guard the channels used in that sector or area. The CG also has the net 100’s and net 400’s channels to use as command and control.
If someone were to use marine radio on land and select a channel not used by the CG, commercial, or noncommercial user it would easier to avoid detection. In an area like the Chesapeake Bay these channels are so crowded on summer weekends that general chit chat would most likely sound like pleasure boaters. Sector Baltimore does transmit message if they receive unauthorized users on channels being monitor, but I can’t speak for all other sectors. I only travel in a few different ones a few times a year.
Larry