http://www.trail-camera.co.uk/Trail-Camera.htm
plonk one of those at a suitable point, midway down the lane, (so as not to snap anyone using an end to do a 3-4point turn, but Driving down it).
id not advise confronting people driving down it, your not law enforcment, or council staff who's duty is the enforcement, so the risk of a thumping or harrassment charges are possible.
If the council could/would change the signs to the "red circle with car/motorbike" no entry ,with the "except for access" cavat that is the best you can hope for.