Players and coaching staff from both teams came together minutes before kickoff at the Diego Armando Maradona stadium to pose in front of the slogan after a day of protests across the world.
Barca beat Napoli handily by a final score of 4-2 to reach the last 16 of the Europa League, a competition the Spanish side have not been involved in since 2004. The first leg ended 1-1 at Camp Nou on Feb. 17.
Elsewhere in the Europa League on Thursday, Ukraine international Ruslan Malinovskyi unveiled a "No war in Ukraine" T-shirt after scoring for Atalanta against Olympiakos as the Italians progressed to the next round.
In the Europa Conference League, Slavia Prague wore jerseys with the message "We stand with Ukraine" in a winning outing against Fenerbahce in UEFA's third-tier competition.
The actions follow Ukrainian President Volodymyr Zelenskyy's decision to impose martial law across the country earlier in the day after Russia launched land, sea and air attacks on the country.