Maryland law addresses both possession of a, “Gambling Device,” and playing a, “Gambling device,” and both of those have penalties that go along with them. Once again, this is probably just an example of a state throwing a law on the books to protect its own gambling interests, given that Maryland has a lottery as well as land-based casinos in a few different cities.

The code that we cited on our restrictions page.
Reads like this:
§ 12-102. Betting, wagering, gambling, etc.
(a) Prohibited.- A person may not:
bet, wager, or gamble;
make or sell a book or pool on the result of a race, contest, or contingency;
establish, keep, rent, use, or occupy, or knowingly allow to be established, kept, rented, used, or occupied, all or a part of a building, vessel, or place, on land or water, within the State, for the purpose of: (i) betting, wagering, or gambling; or (ii) making, selling, or buying books or pools on the result of a race, contest, or contingency; or
receive, become the depository of, record, register, or forward, or propose, agree, or pretend to forward, money or any other thing or consideration of value, to be bet, wagered, or gambled on the result of a race, contest, or contingency.
(b) Penalty.- A person who violates this section is guilty of a misdemeanor and on conviction is subject to imprisonment for not less than 6 months and not exceeding 1 year or a fine of not less than $200 and not exceeding $1,000 or both.
Most of this verbiage would seem to pertain to operators as opposed to players, except the, “Bet, wager or gamble,” could be seen as pretty clearly applying to players.
There have been a few examples of illegal gambling activity over the years to be addressed by law enforcement throughout the state, but all of those examples have concerned either sports betting or physical operations of one kind or another.
As always...
...we can find no example of anyone to ever face legal consequences for acting as a mere player gambling online and this is extremely unlikely to ever happen. With that said, as an increasing number of states bandy about the possibility of legalizing and regulating their own online gambling operations, it would be a surprise not to see Maryland eventually join the fray.

For one thing
Maryland has physical casinos that are licensed and regulated through the state, which is basically step one into making a move into online more likely. The second reason we see this as a possible eventuality is that three of the four states with fully legalized online gambling are geographically pretty close to Maryland, such that it might see itself losing potential revenues to them, particularly Pennsylvania.
In any event, the majority of internet casinos that offer their services to the United States also offer those same services to residents of the State of Maryland, and here are some of them below: