Sen. John Fetterman, D-Penn., on Thursday tweeted out a photo acknowledging 4/20, an unofficial holiday dedicated to smoking and celebrating marijuana. 

In the photo, the hoody-wearing senator is holding up a flag bearing the phrase, "It’s 420 somewhere." 

The "420" appears to resemble a marijuana joint. Marijuana leaves are scattered throughout the flag. 

"It’s 4:20 on 4/20. That’s the tweet," wrote Fetterman. 

Hours before, the senator posted another tweet signaling his support of legalizing cannabis. 

"You know what goes great with some weed? A Union," Fetterman wrote in response to a story about marijuana dispensary workers seeking to unionize. 

The origins of the 420 holiday are unknown, but many believe it originated in California in the 1970s when teenagers would ritualistically smoke marijuana at 4:20 each day. The term 420 ultimately became synonymous with the drug and was promoted by bands like The Grateful Dead. 

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Fetterman, elected to the Senate in November after beating Republican opponent Dr. Oz, has been a staunch supporter of cannabis legalization, both in his role as Lt. Gov. of Pennsylvania and Mayor of Braddock, Pa. 

On the campaign trail, Fetterman called on President Biden to deschedule marijuana from its classification as a Schedule I drug and work to decriminalize it. 

"It’s long past time that we finally decriminalize marijuana," Fetterman said in a press release. "The president needs to use his executive authority to begin descheduling marijuana."

Fetterman returned to the Senate Wednesday following a lengthy stay in the hospital for clinical depression that began in February. 

Fox News’ Andrew Mark Miller contributed to this report.