I recommend paying it early, since it probably doesn't go on your traffic or driving record (at least that's the case in my state), and if you wait it will cost more money. If you fight this, you'll pay court costs as well and/or attorney fees.
My guess is that some busybody called the cops on you. If you can find out who it was, look up a bunch of ordinances and then get some paybacks when they do something like this.
Unless Maryland is unusual, there are no court costs and no need for an attorney to fight a simple parking ticket. Just show up and tell the truth and be respectful.