Mariah Carey's star on the Hollywood Walk of Fame was vandalized over the weekend ... in a much more subtle way than Donald Trump's.
A rep for the Hollywood Chamber of Commerce tells us ... they called the LAPD Sunday and they gave cops a lead -- someone on Instagram claimed responsibility.
We're told it cost $1,500 to restore the star. Hollywood Historic Trust has already had it cleaned up.
Cops are on the hunt. They're pulling surveillance video. The investigation is for felony vandalism.
No word if James Otis has an alibi.