What makes a great poster is what the poster has to say, and whether it says it well with eye-catching creative.

But where the poster is placed can be an integral part of the message.

That was the case for a recent run of posters for Audi in Germany.

The aim of the campaign was to talk up the automaker’s “side assist” system, which claims to reduce a vehicle’s blind spots with more effective side mirrors.

The creative team at Hamburg's Philipp und Keuntje came up with the idea of illustrating how blind spots can keep drivers from seeing vehicles approaching from behind.

Rather than put the posters up on flat surfaces, they came up with creative designed to take advantage of the corners of walls.

The reason became obvious once the posters went up.

Looked at head on, the posters show a typical rear view mirror. In the mirror is a picture of an empty road. But walking a bit to the left, the poster opens up and one sees an entirely different picture: In the mirror is the same scene except in the center is a motorcycle speeding up from behind.

The section of the poster with the motorcycle was on the side wall.

Also coming into sight are the words: “See more. Audi side assist.”

Philipp und Keuntje's Susanne Hellpoldt says the challenge was to come up with something that was visually arresting to illustrate a technology that in itself was not at all dramatic.

"We always try to create something interesting for very technical and demure issues like a side assist mirror,” she says.

The ads ran near Audi dealerships throughout Germany, and Hellpoldt says Audi dealers reported a 35 percent boost in demand for cars with the side assist system.