Advertising on Vehicles

I thought there was a club rule that forbade vehicles showing advestisments such as those used for commercial enterprises (builders/carpenters etc etc) coming on site but I have seen an increasing number.  Some rules it appears can be at the descretion of the site wardens but according to my site directory not this one.  If so I guess wardens are literally turning a blind eye. Last site we visited there was one that arrived and stayed for the week with a van in tow.  Am I alone in spotting these???