For fans of the band, every day is Guster Day. But the City of Boston is only committing to one day, and that’s Thursday. Mayor Marty Walsh has declared Jan. 15 to be Guster Day in honor of the band that was formed two decades ago by Tufts freshmen. Adam Gardner, Ryan Miller, and Brian Rosenworcel will be in town to celebrate — and to promote their seventh studio album “Evermotion” — with a few surprise busking sets and a performance at the Greenovate Boston 2014 Climate Action Plan Launch Celebration at the Artists for Humanity’s EpiCenter in South Boston. “I’m not confirming or denying any location where we might play,” Gardner told us the other day. “But when we started out, we busked in Harvard Square and sold a lot of demo tapes and CDs out of our guitar cases.” He said it’s cool to be recognized as a Boston band. “A Guster day in any other city would be weird. We absolutely identify as a Boston band even though we were really never part of the scene,” he said. “For a while, we were kind of the house band at the Paradise. Any time a national act came through and needed support, we played.” Gardner said some of his favorite bands hailed from Boston. “Bands like Morphine, the Lemonheads, Juliana Hatfield, Buffalo Tom, Push Stars, Letter to Cleo, and Orbit,” he said. “You remember Orbit?” Guster’s new CD, produced by Richard Swift, comes out Tuesday.