An anti-Semitic note was found on a billboard at the Brooklyn Jewish Children’s Museum on Thursday evening, and police are now investigating it as a hate crime, cops said.

The post-it note with “Hitler is Coming” scrawled on it was found on a billboard that was designed for visitors to leave positive messages at the Crown Heights museum at about 8 p.m., cops said.

Visitors alerted police to the anti-Semitic note, who in turn notified the hate-crime task force, authorities said.

After seeing the hateful message, Chabad rabbi Mordechai Lightstone lamented in a message on Twitter.

“This is just awful,” he wrote. “An interactive sign in front of the the Jewish Children’s Museum in Crown Heights asking people how they would transform the world was defaced with Antisemitic graffiti!”

Soon after the message was reported, Gov. Cuomo ordered the state police to assist the NYPD in their investigation.

“We have zero tolerance for anti-Semitism, discrimination or hate of any kind in New York, and no person should ever feel threatened because of their religious beliefs,” Cuomo said in a statement.