Google (Nasdaq: GOOG), the giant of web search and advertising, is taking out ads in an unexpected sector – billboards – to tout its $50 per year application suite for business workers.

in New York, San Francisco, Chicago and Boston in August to promote the “apps,” the Associated Press is reporting. But they will hardly be static. Google plans to display a different message each weekday.

“People don’t necessarily think of Google when it comes to how we can help companies,” Michael Lock, director of sales and operations for Google’s enterprise division in North America, told the AP.

However, for now, Google doesn’t plan to advertise its business applications in other offline media like magazines, newspapers, television or radio, said Andy Berndt, managing director of the company’s creative labs.

Google’s targets? Apps providers by the name of Microsoft and IBM.