What is the second oldest form of advertising in the world? Billboards (word of mouth was first). In it's earliest form billboards were drawings on the cave walls of prehistoric man. Today, they're high-resolution color graphics seen along virtually every expressway and state highway around the world. We love billboards. When done well, they communicate a sales message in a clear and concise way. Sometimes they're clever, and Sometimes they're disturbing, but anytime they're done well you take notice.