The compost year in the bin

The last week in June and we have had a change from all the weeds that have dominated the material left in the Community Reception bins during the  month. Lettuce and beans have suddenly appeared from one plot holder. The lettuce has been diverted to the wormeries to give the worms a treat. I have had convention plastic wormeries for over ten years but this year we have installed a Subpod in ground wormery.( Follow the link Wormeries ) I was not sure about this thinking all the worms would go on a walk about  but this has not proved to be the case and they are busy producing good compost. 

The worms behaved well but some plot holders removed the Do NOt Use Signs from two bins and filled them with weeds and dumped a builders bag of weeds on the site. Has anyone out there come up with a method of stopping people abusing the system on open access sites?