I wish...
Very few area's I encountered had markers. Occasionally they would spring up and then be gone within a couple of season's. Around France its even harder to spot them amonst all the pot markers. Fisherman seem to treat Danger areas as their protected grounds.
But then I often had a chart plotter (GPS moving map) and would be very clear of the boundaries. (But then I might be re-opening the DR vs GPS debate...)