The sign, completed Friday by artist David Lee of Arvada, shows a grinning, cartoonish Obama and bears the words: "PRESIDENT or JIHAD?"
Underneath the image is a yellow square with the phrase, "BIRTH CERTIFICATE, PROVE IT!"
The words "WAKE UP AMERICA! REMEMBER FT. HOOD" appear at the bottom of the billboard at Wolf Interstate Leasing and Sales, about seven miles west of Denver.
General Manager Wayne Means says the dealership has seen strong opinions about the sign, both for and against it.
The left-leaning advocacy group MoveOn.org called the billboard "racist" and is asking customers to boycott the business.
Dealership owner Phil Wolf was unavailable for comment.