Former research assistant Heidi Liu passes along link with this tidbit:
Colgate normally gives out small product samples at annual events like “Oral Health Month” to remind target consumers, especially kids, to take better care of their teeth after eating sweets. This method does not drive strong results as most consumers tend to forget the message, even if they have collected the samples. Instead of giving away product samples, ice cream and cotton candy were given out. The stick carrying the ice cream and cotton candy carries a hidden message. Once consumers are done the message printed on the tip of the stick shaped like a toothbrush reveals “Don’t Forget” with the Colgate logo. This simple message effectively reminded consumers to brush their teeth.
Picture of stick is here.