Check out this defacement job that happened on a billboard on the corner of Centinela Ave. and Santa Monica Blvd. here in Los Angeles -- where an advertisement for Susie Essman's Caftan from "Curb Your Enthusiasm" went up sometime this past week in an homage to the show.

If you're unfamiliar, her Susie character from 'Curb' started her own business and threw up a billboard to advertise it -- which got vandalized on TV with people drawing penises around her face ... something that delighted LD.

As it turns out ... HBO commissioned an exact replica of this fake TV billboard to go up in real life as well, and to nobody's surprise -- it was also defaced, just like on 'CYE.'

If you're wondering who's responsible for the tag job ... we have an answer. There's an activist art collective called INDECLINE -- and they say they're the ones who pulled this off. We're told this went down early Friday morning ... and they even filmed themselves doing it.

The reason ... they say they were just fulfilling a wish from none other than 'Curb' star Jeff Garlin himself ... who responded to someone this week after the billboard went up and wrote, "Someone should put a d*** up there. Maybe two." Welp, that's exactly what INDECLINE did.

The collective tells TMZ, they give Larry a lot of credit for forming their sense of humor and sensibility ... so they feel they were paying homage to him by carrying out this stunt.

They add, "A few nights ago, we watched in awe as one of our favorite pastimes, 'billboard liberation, was incorporated into the latest episode. We received a flood of texts and DMs about the existence of the billboard in Los Angeles and even saw that Jeff Garland was on Instagram calling for it to be altered."

INDECLINE goes on ... "So, as a thank you to Larry David, for his contribution to the field of art imitating life, we give you our contribution to the practice of life imitating art."

The obvious question is ... are cops gonna look into this? We're told by law enforcement sources that, at this point, nobody has called in just yet to report a crime -- so as far as they're concerned ... there's not much to do about this for now.

BTW, these are the same guys that did the naked Trump statue years ago ... so there you go. They're known for stuff like this -- and they didn't disappoint here either.