Police are investigating who wrote “KKK Meeting Today” on an electric construction sign board in South Boston on Monday.

The police department’s Civil Rights Unit has taken over the investigation after a Boston police officer saw the sign in the area of D and Cypher streets in Southie at around 7:40 a.m. on Labor Day.

The electric construction sign board belongs to a private construction company, whose name was blacked out on the police report. The construction firm was listed as a victim for the vandalism incident.

Whether a hacker took control of the sign board or if an employee from the construction company wrote the phrase is “part of the investigation,” according to a Boston Police spokesperson.

A police officer in Southie came across the “Electric Construction Sign Board with a notification that read, ‘KKK Meeting Today,’ ” reads the police report.

The officer took a photo of the sign and notified the police district’s supervisor. A sergeant responded to the scene and was able to disable the electric sign.

Massachusetts State Police was notified about the incident and responded to the scene, as well as Massport.

Elsewhere in Massachusetts over the long weekend, police on Martha’s Vineyard are looking into who put up signs for the white supremacist group Patriot Front.

“We are looking for any information regarding who posted these signs around town overnight,” the Oak Bluffs Police Department posted. “Please contact an officer at 508-693-0750 or send us a direct Facebook message.”