The rules say:

"Virginia's Territorial Sea, plus all of the creeks, bays, inlets, and tributaries on the seaside of Accomack County, Northhampton County (including areas east of the causeway from Fisherman Island to the mainland) and the City of Virginia Beach (including federal areas and state parks fronting on the Atlantic Ocean and east and south of the point where the shoreward boundary of the Territorial Sea joins the mainland at Cape Henry)."

I take it to mean that it is 0 to 3 miles from the beach along the oceanfront and seaside of the Eastern Shore. Its been a while since I have done the coastal thing and I remember it was always a chore to figure out if we were too far out.

Is there an easy way to make sure you stay legal (like markers or buoys)?

Yes, 0 to 3 miles out from false cape north and cape henry south. Your best bet is to get a fishfinder with GPS, the 3 mile mark is usually indicated on the screen. Don't go by the boats around you, there is usually a group that pushes the 3 mile limit!

and if you are going by those boats, make sure you are faster!