This is actually from another site (to save me typing it) but I do know, from my own knowledgs having been in marketing for around 30 years (!) that this explanation is 100% accurate. It was a superb campaign and a great idea.
In the mid-1970s, cryptic posters started to appear in bus shelters all over Britain. They showed a small girl and the message: �My name is Amy, I like slugs and snails�. That�s all. No brand name, no logo, no attribution of any kind. The posters stayed up for weeks, so someone was making a massive advertising investment. But for what purpose?
Speculations in the popular press boosted casual interest into a national obsession. Finally, a press release published the results of a survey showing the high levels of recognition this poster had achieved. It also revealed the name of the lavish advertiser - Adshel, the company which owned the poster sites. They put up nonsense ads as a way of demonstrating the strength of its medium; Amy was the daughter of Adshel's sales director.