In the secret code of New York gangs, texting two thumbs up doesn’t mean everything is OK.

It means you’re a member of the Harlem Crips, a ruthless band of hoodlums who have terrorized upper Manhattan for decades, according to police.

They say violent city street toughs have turned to cutesy emoji and other digital imagery to communicate with each other, using seemingly innocuous symbols as tools of murder, assault, rape and robbery.

“Social media is something the juveniles and youth are constantly using,” said NYPD Sgt. Leo Nugent of the Bronx Gang Squad, noting that the gas pump has become a universal symbol for “gang.”

“If I’m in a gang mode, I’ll put that up,” he said.

The Crips opt for the two thumbs-up emoji, with the knuckles facing each other, because they resemble the letter “H.”

Their longstanding rivals, the Bloods, signal their affiliation with an image of a magician’s top hat.

They even go after each other with emoji, posting other gangs’ symbols upside down as a sign of disrespect.

And they livestream video from their opponents’ turf on Snapchat, a type of taunting known as “cyberbanging.”

Gangs have learned to avoid Facebook, which police have scoured for years for evidence used to lock up suspected leaders.

“They call Facebook ‘Fedbook’ now, because if you talk on Facebook, the feds will be monitoring,” Nugent said.

Gangbangers now prefer WhatsApp, CoverMe, Kik Messenger and Yubo — a dating app marketed to teens — where their messages quickly disappear, making it harder for cops to track them, according to lawmen.

“They’re pretty smart,” said Detective Belinda Delgado, also with the Bronx Gang unit. “WhatApp — the minute you delete it from your phone, it disappears.”

Messages sent in chat apps are not visible to the public, so there’s no way for cops to monitor conversations.

Nugent said gangs are using emoji to recruit new members and to demand they commit crimes.

He said gangs might order new members to run a credit card or check scam, using digital symbols of a man running, a money bag and a credit card.

“Members we have identified will ask for anyone who is 18 and over and who has a valid ID to private message them,” Delgado said.

Gang activity is also carried out on gaming consoles, according to Nugent.

In one robbery, a Crip set up a purported cellphone sale while chatting via PlayStation. When the victim showed up, someone pulled a gun on him and robbed him, Nugent said.

“In these chats sometimes people sell items, sneakers, headphones or cellphones, etc.,” Nugent said. “The gamers can pull up pictures of each other, so they know who they are communicating with.”

Police rely heavily on confidential informants (CIs) to fill them in on gang methods, according to Delgado.

“A CI who says, ‘Hey, our set uses Snapchat, and we communicate there when we have meetings’ . . . when we have a problem he gets us the screenshots.

“Without a court order, we can not monitor in real-time.”

The NYPD has enlisted parents to monitor potential gang activity on social media, and teaches them what to look for at gang-awareness seminars.

“I can’t go to every kid and look through his phone, but the parent can,” Nugent said.

Police said teens with big social-media followings should be a red flag for parents.

“If your kid has 3,000-5,000 friends — that could be a problem if you live in a certain neighborhood,” Nugent said.