The Flash just gave Ralph Dibney (Hartley Sawyer) an official insignia, which was worn by the character in the Justice League Unlimited series. Like Barry Allen (Grant Gustin), Elongated Man now has his own emblem in the Arrowverse.
Hartley Sawyer's Elongated Man has been on the show since the fourth episode of the fourth season, "Elongated Journey Into Night", when Ralph first developed his elastic abilities. At the beginning, Ralph was irresponsible and selfish, and a person who Barry didn't believe he could trust due to issues from their past. However, Barry decided to give Ralph a second chance and made him a member of Team Flash. Ralph's character has come a long way since that day, as he's grown to become one of the Flash's most reliable allies.
In The Flash season 6, episode 6, titled "License to Elongate", Barry and Joe (Jesse L. Martin) hatch a scheme to surprise Ralph by honoring him a ceremony and making him the new protector of Central City. After going on a dangerous mission connected to the Sue Dearbon case, Barry and Ralph make it out alive and save the city once again. At the end of the episode, Barry and Joe officially recognize Ralph for his accomplishments at CCPD in front of the press. Ralph is given an insignia with the letters "EM" on it, which will now be worn as a part of his "Elongated Man" costume.
Fans of Cartoon Network's Justice League Unlimited animated series may recognize the logo on the emblem. It was worn by the Elongated Man in the show, which ran from 2004 to 2006. To this day, Justice League Unlimited remains one of the most beloved cartoons based on the world of DC Comics, so it seems fitting that the Arrowverse would find a way to honor a design from the fan-favorite series.
Also, the moment where Ralph receives the emblem symbolizes his transformation into a full-fledged superhero. It goes to show that Ralph has evolved into the hero from the comics, even though The Flash is still building toward his biggest story. Regardless, Barry has accepted Elongated Man as the hero that Central City needs, which is an important step for Team Flash. While Barry has chosen Cisco (Carlos Valdez) to be the new leader, it's Elongated Man who he wants to watch over the city after Barry dies in the Crisis. Whether or not this will happen may depend on both the Crisis and the outcome of his encounter with Ramsey (Sendil Ramamurthy) in the closing seconds of the episode.