The "OK" hand gesture is a hate symbol, the Anti-Defamation League says.

It is commonly used by alt-right groups, according to the ADL, and has become linked to white nationalism.

CNN reports that a man accused of killing more than 50 people at two New Zealand mosques earlier this year flashed the "OK" hand gesture during a court proceeding.

"We believe law enforcement and the public needs to be fully informed about the meaning of these images, which can serve as a first warning sign to the presence of haters in a community or school," Jonathan Greenblatt, ADL's CEO, told CNN.

Other hate symbols ADL has added to its list include the "Happy Merchant" and "Moon Man" images, as well as the bowl-cut hairstyle worn by Dylan Roof, who killed nine black people in a South Carolina church in 2015.

The "Happy Merchant" image "depicts an extreme stereotype of a Jewish man rubbing his hands together, which is meant to symbolize greed," CNN reported. The cable news network says the "Moon Man" image "is a play on a 1980s era McDonald's commercial that featured a man wearing a crescent moon costume. White supremacists use the character to make videos where he raps using racist rhetoric."

ADL has a database on its website the lists various hate symbols that are commonly used.