You can have two without a license. That's all I have and I've been able to catch enough for my wife and I to eat. If I had a boat, I would probably get the license so I could have more gear out.
Here's the rule for marking the gear;
Buoys of any crab pot, eel pot, gill net or ordinary crab trotline, and an offshore stake of any crab trap, used for recreational purposes, shall be marked legibly with the licensee's last 4 numbers of his/her social security number or driver's license number, preceded with the letter "R"; these figures must be at least 1 inch in height. [4 VAC 20-670-40].
You are also supposed to report your catch annually to VMRC.
Any person catching finfish or shellfish using a recreational gillnet, cast net, dip net, crab pot, crab trap, crab trotline, eel pot, or any other recreational license established by Regulation 4-VAC-20-670 must report annually on forms provided by the Commission: the weight and species harvested, location of harvest, days fished and amount of gear used.
Here's the link to the form;
http://mrc.state.va.us/forms/recform.doc. I do this although I doubt they'd come after me if I didn't.