Gaster, a Vietnam veteran, told FoxNews.com he built his now 28-year-old business from the ground up.

“I started on my own,” Gaster said. “The government wasn’t there. We work long, hard hours and what he said is an insult to any businessman.”

The sign has been criticized for its harsh language, but Gaster said that the rough words were necessary.

“When I heard what he said, I said ‘I’m going to give him an answer in Chicago language–something he’s used to,'” he told FoxNews.com. “If I would have said ‘Dear Mr. President…’ there wouldn’t have been as strong of a response.”