New Gun Billboard Flaunts Message That AR-15 Rifles Are 'Pure American' -- Like Baseball, Apple Pie (PHOTO)

As the debate over guns in Chicago wears on, a new billboard is raising eyebrows for its controversial message that suggests AR-15 rifles are as "Pure American" as baseball and apple pie.

The advertisement, visible from the outbound I-55 Stevenson Expressway on the city's Southwest Side, is for the gun parts company, Slide Fire. According to Slide Fire's website, its gun stocks enable users to modify semi-automatic rifles for "bump fire" -- a tweak that uses a gun's recoil action to fire multiple shots quicker.

"It sprays like a fire hose," Slide Fire sales and marketing manager Brandon Renner told CNN in a 2013 interview when the new product debuted. "We recommend no more than 30 rounds on the belt, but one person could make it as big as they want."

Annette Holt, who lost her son to gun violence in 2007 and went on to found the anti-gun violence group Purpose Over Pain, told Fox Chicago the billboard is "outrageous."

"If you just want to advertise a gun, advertise a gun, but don't put things with it that are going to encourage young people -- especially teenagers and children -- that that's what goes together with it because it doesn't it," Holt said.

The billboard also features the American flag, a Second Amendment symbol, the ichthus -- the fish commonly used to symbolize Christianity -- and the Statue of Liberty.

When reached for comment, Chicago Police told Fox only that "military-style weapons belong on the battlefield and not on the street."

Though machine guns are illegal in the U.S. for most people, the Bureau of Alcohol, Tobacco, Firearms and Explosives has ruled products like those from Slide Fire are entirely legal since the weapons are technically semiautomatic, according to CNN.

Gun dealer Louie Asanon, who sells the Slide Fire stock, told Fox users just enjoy the fun of rapid-fire shooting and "it's just another feature of bearing arms."

The same billboard generated similar controversy when it when recently went up in Harrisburg, Penn.