A "billboard advertisement" refers to a large sign or poster displayed in a public area, such as alongside a road, to advertise a product, service, or event. Full definition
Think of it as a small billboard advertisement for you and what you do. (topresume.com)
Of course, neither math nor context play as well on billboard advertisements as a big number. (automobilemag.com)
Around the exterior of the body of the water tower, they owner sells huge highway size billboard advertisements that sell for top dollar. (nakedpastor.com)