The large and iconic anti-gun violence billboard that has overlooked the Mass Pike near Fenway for 20 years is coming down.

The billboard, which is 252 feet long by 20 feet tall, is affixed to a Lansdowne Street garage. Developer John Rosenthal, co-founder of the Stop Handgun Violence, which is the group behind the billboard, sold that garage to the Boston Red Sox two years ago. The team’s ownership gave him a two year lease that allowed him to keep the billboard on the structure. That lease term is up. Rosenthal said the sign could be taken down anytime in the next two months.

“There isn’t a definite timeline,” he said.

Rosenthal said he sold the building because the deal “made sense and we had a very willing buyer.” He believes the billboard, which currently has a message advocating for an assault weapons ban and a running counter of the number of Americans killed by gun violence since the Sandy Hook massacre in December 2012, is the largest horizontal billboard in the country.

“It’ll be sad to see the huge billboard come down after all these years, but thanks to our new creative team and outdoor advertising company partners this campaign will continue and our message will live on and be seen by more people in many new locations,” said John Rosenthal, co-founder of Stop Handgun Violence and President of Meredith Management. “In 1995, we put the billboard up to change the dialogue on gun violence in America and ultimately change gun laws and make Massachusetts a national model for gun violence prevention.”

He added, “Over the last twenty years, we have worked with law enforcement, community organizations, elected officials, survivors and a variety of faith based groups to effectively change the historically polarized debate to one that now respects gun rights and gun violence prevention laws and initiatives. As a result we’ve enacted the most effective gun laws in the nation and we’ve saved countless lives and endless grief from preventable gun violence.”

Rosenthal’s group plans to feature anti-handgun messages on more than two dozen billboards in the Boston area. A permanent sign will be built on the Fenway Center development built on Mass Pike air rights in Kenmore Square. Rosenthal is the developer for that project, which will cover the Pike between Brookline Ave and Beacon Street and surround the new Yawkey commuter rail station. Construction on the Fenway Center project will begin at the end of the year, said Rosenthal. The project is expected to be completed in three years time.

In the past, Stop Handgun Violence billboards, according to Rosenthal, have included provocative and at times irreverent messages about responsible gun ownership, gun trafficking, the NRA’s control of Congress and the real life consequences of gun violence.