It had been YEARS since I last saw one. These signs were a fad that peaked back in the mid-80s (I remember mom having one for my brother Dan when he was a baby, circa 1987). They also led to a host of humorous imitators (my favorite being "Mother-In-Law In Trunk"). I can't help but think of the Simpsons episode where Marge Simpson bought one hoping it would stop people "intentionally ramming our car."
