One of the phrases scrawled on a bullet casing belonging to Charlie Kirk assassin Tyler Robinson is a lefty Italian anti-fascist phrase associated with World War II.

“O bella ciao, bella ciao” was written on one of three unfired casings recovered after Kirk’s killing, Utah Gov. Spencer Cox said during a press briefing Friday morning in announcing the arrest of the 22-year-old suspect.

The slogan is the title of an anti-fascist song popularized after World War II by left-wing Italian partisans.

Singing the song is a hallmark of Liberation Day in Italy, which is celebrated every April 25 and commemorates the fall of Benito Mussolini’s fascist regime — though there is no evidence that the song was known or popular at the time of the conflict.

The slogan has been embraced by the global left and was famously sung by trade unionists in May 2023 to taunt conservative Italian Prime Minister Georgia Meloni.

Kirk, a popular conservative commentator, was shot and killed Wednesday on the campus of Utah Valley University, leading to a furious manhunt that led to the capture of his accused murderer.

The message engraved on the casing of the bullet that killed Kirk is used in trolling and “furry” subculture — and experts told The Post on Friday it was written by someone likely chronically online.

The casing had the words, “Notices Buldge OWO what’s this?” on it, according to an arrest affidavit.

The string of words can be used for trolling — and connected to online furry and role-play groups, digital culture experts said.

“Notices buldge” is a meme that shows two guys, including one with cat ears on, sitting across from each other over the computer in what could be perceived as an instance of catfishing, said Queens College media studies Associate Professor Jamie Cohen.

The likely joke is they are both pretending to be something they’re not, he said.

“What’s this” at the end of the message is referring to the person on one end of the meme spotting a bulge as the realization sets in this was a scam.

Meanwhile, “OWO” is an emoticon that displays a cutesy animal face with big eyes and a little nose.

It can be a copypasta, which is a block of text meant to be copied and spread, said another digital culture researcher, Alex Turvy.

“More than anything, it sort of demonstrating that you speak the language of the Internet,” the sociology PhD said. “It’s sort of an inside joke and referencing it a marker of who you are. That you spend a lot of time online.”

He noted “OWO” is common in online role play and the subculture of “furries,’’ or people who take on animal persona.

Another unfired casings had the words, “Hey fascist! Catch!” as well as an up arrow, a right arrow and three arrows pointing down.

The arrows may refer to how players of the video game “Helldivers 2’’ move their controllers — to unleash bombs, the New York Times reported.

The third unfired casing was scrawled with, “if you read this, you are gay lmao,” authorities said.