This is a gag that was in one of my sketchbooks for years before I drew it up, because I didn't think people would go for a joke about possessive apostrophes! I was wrong. It was in the last issue of Private Eye and I have had a very good reaction to it.
A Private Eye reader contacted the magazine to say that it reminded him of this postcard which was on sale for many years at Birling Gap, near Eastbourne. Clearly they need to read this.