For Red Sox fans, the association is automatic: when a home run sails over the Green Monster, you see the red, white and blue Citgo sign flashing in the background.

But now, the sign’s days as a Boston icon could be numbered, because Boston University is selling the property that sits directly underneath it.

"For people on a national stage, the Citgo sign says Boston," says Greg Galer, the executive director of the Boston Preservation Alliance. "When you think of what images the national media throws up for Boston, it’s Old North Church, the swan boats, the Citgo sign, the State House. It’s right up there."

Ideally, Galer says, BU--which is selling several properties in Kenmore Square--would have taken steps to protect the sign's future. 

"Instead of putting out a [Request for Proposals] that says, 'Anybody who wants to bid on this property, bid on it,' they could say, 'We’ll only entertain offers that respect the Citgo sign.,'" Galer says.

Such a step could have dissuaded potential buyers, however. And BU chose not to take that approach.

Now, Galer's group is pushing for the sign to be designated a Boston landmark, a status that would require a city review of anything that might change it.

"This is an important part of what makes Boston Boston," Galer says. "So as you start chipping away at that, at what point is Boston not Boston anymore?

Of course, some people would say that Kenmore Square hasn’t been Kenmore square for years. Gritty venues like the famed Rathskeller are long gone, replaced by the Hotel Commonwealth and other upscale developments.

Writer Louisa Kasdon recalls seeing the Citgo sign from her childhood bedroom on Bay State Road. If it’s taken down, she says, the last vestige of her old neighborhood will disappear.

"Kenmore Square’s just another place," Kasdon says, imagining the sign's removal. "It’s another place. It has a nice T station, it has Fenway Park, it has nothing kind of imaginative and cool to set it off."

Naturally, Citgo wants the sign to stay put—and it’s mounting an aggressive PR push, including a slick online tribute video that touts the sign's local significance.

There’s a note of irony there. Back in 1982, Citgo was poised to tear the sign down, until the city of Boston stepped in.

At the time, the company opposed an effort to make the sign an official landmark. If it had embraced that option, the current crisis might not be an issue at all.