The New York Mets are gearing up for the golden anniversary of their 1969 World Series win — with a marketing push that’s aimed at social media-obsessed millennials.

In a little-noticed filing last week with the US Patent and Trademark Office, the Amazins submitted a second request to trademark “LGM” — the popular hashtag on Twitter and Instagram that’s shorthand for “Let’s Go Mets.”

The one-page application, spotted by eagle-eyed trademark lawyer Josh Gerben, seeks to extend the club’s 2016 filing to protect #LGM on assorted merchandise like hats and T-shirts.

The new application wants to secure LGM protection for “education and entertainment services,” including at “museums,” “baseball exhibitions,” and “seminars in the field of sports and cultural history.”

Experts say it’s a clear bid by the team to promote their social media presence during the 50th anniversary of their stunning World Series victory over the Baltimore Orioles, scheduled to take place in June.

June events marking the 50th anniversary are expected to include a documentary directed by Ed Burns on Mets’ Hall of Fame pitcher Tom Seaver.

“It was a big moment, not just for the Mets but for baseball in New York,” Joe Favorito, a sports marketing consultant, said of the ’69 win. “If you build out anything, especially when acronyms are being used for everything, you need to protect it,” Favorito added.

#LGM has been gaining traction on social media since the 2015 playoffs, when the Mets lost in the World Series to the Kansas City Royals. It’s shorthand for a catch phrase that was only created during the Mets’ second — and last — championship season in 1986 as a song to help drive the team and its fans to victory.

The song, which has copyright protection, was composed and produced by Shelly Palmer based on an idea from advertising legend Jerry Della Femina and two of his colleagues.

In an interview with The Post, Della Femina joked that the team’s disappointing performance of late should prompt them to seek protection for “LGMA,” which he said would stand for “Let’s Go Mets, Already!”

Della Femina recalls getting the Mets’ advertising assignment in 1980 — the first year his former Lafayette High School classmate, Fred Wilpon, acquired a 1 percent stake in the team and became its president.

The ad man’s initial theme for the Mets — “The Magic Is Back” — was tongue-in-cheek for a team that ended the season with 67 wins and 95 losses, he said.

“It wasn’t about the Mets so much as the joy of watching baseball again,” Della Femina said.