A Hair Raising Experience

Among the first people to use secret messages were the Greeks, although some of their early techniques were a bit inconvenient. For example, Greek generals would have the head of a messenger shaved, tattoo a message on their scalp, wait for their hair to grow back and then send them on their way!

You can see that this method had some drawbacks: you would have to wait for at least a couple of weeks before the unfortunate messenger had grown their hair back, and pretty soon their scalp would be so full of tattooed messages that they wouldn't be able to fit any more on!