It’s the smoking gum.

A tourist was caught on camera slapping a wad of gum to a Lower Manhattan street sign Wednesday — a day after The Post revealed visitors on double-decker tour buses have been plastering the placard with the sticky substance as they roll underneath.

The confectionery vandal was seen slyly reaching up and adding a new piece to the mess of old chewy candy on the sign outside City Hall along Broadway at Park Place as the open-roof TopView coach drove slowly below.

As The Post reported Tuesday, sightseers on the tours have already gunked up that sign — and another nearby — with their gum, as well as stickers and discarded headphones smooshed into the goop.

The city earlier Wednesday promised to replace the signs within two weeks.

TopView did not immediately respond to a request for comment.

Two other companies, Gray Line and Big Bus Tours New York, also offer roof-less double-decker tours of the Big Apple on similar buses.

Big Bus said it tries to curb such behavior by having tour guides accompany drivers.

“A driver of a 45-foot-long vehicle in Manhattan cannot be asked to monitor a small screen for potential customers standing up,” said Charles Nolen, the company’s general manager, said in a statement.