There are no laws in Maryland that restrict scanner use in vehicles.
Columbia is in Howard County which operates an 800 MHz P25P1 simulcast TRS. EMS is integrated with the fire service in the county. Medical consults are conducted on the UHF MED channels and on MED channel crosslinks on the local trunked radio system, thus can easily be locked out or not included in scanner programming. Both the county police and the local state police barracks dispatch talk groups are not encrypted, and both are available on the county system. The state's P25P2 simulcast TRS carries some additional traffic including several out-of-the-area state police barracks, Natural Resources Police, and highways traffic management units.
This is the Howard County system:
Howard County Trunking System Profile
www.radioreference.com
Talk groups to get you started:
10961 - County Police District 1
10961 - County Police District 2
10901 - Fire Dispatch
10902 - Fire Ops 1
10903 - Fire Ops 2
11016 - State Police - Waterloo Barrack
The state system (lock out all sites except Howard Simulcast):
First Responders Interoperable Radio System Team (FIRST) Trunking System Profile
www.radioreference.com
BWI has its own system which *may* be receivable in Columbia:
Maryland Aviation Administration Trunking System Profile
www.radioreference.com