A group of 20 to 30 people dressed in black ninja costumes and masks vandalized east side businesses Friday night, causing thousands of dollars in window damage, police said Saturday.

'They were yelling 'Black Knights,'' Milwaukee Police Lt. Milan Stojkovic said.

That's apparently what the group calls itself, and it may have been involved in two to three other vandalism incidents in the past couple years, Police Lt. Michael Robertson said.

Windows were smashed at US Bank, Whole Foods, Qdoba and Bruegger's about 11 p.m. Friday.

Police were investigating whether the vandalism may have been related to a protest earlier Friday evening by a group of self-titled 'anarchists' in the Riverwest area, police spokeswoman Anne Schwartz said.

No arrests had been made. Some acts were caught on business video surveillance.

Police were searching for a green 1992 Honda Civic with a license plate number of 547-HGH, in which some suspects may have fled. Anyone with information is urged to call Milwaukee police at 935-7253.