- "We made a promise to always keep fighting, to be there for each other no matter what-- all of us-- you, me, Roy, Diggle, Oliver, and Felicity."
- —Dinah Drake to Rene Ramirez[src]
The Mark of Four is a code developed by Oliver Queen for Team Arrow in 2019. Based on the four pillars of heroism, it acted as a means of contact for the team after its disbandment. It appears to have a big impact on the team in the years after it was formed.
- "It symbolizes the four pillars of heroism-- courage, compassion, selflessness, and loyalty. We all got them as a reminder that no matter what happened if one of us was in trouble, the other ones would be there."
- —Dinah Drake to William Clayton[src]
According to Dinah Drake, Oliver Queen came up with the Mark of Four sometime before "everything". She mentioned that it represented the four pillars of heroism: courage, compassion, selflessness, and loyalty. It is assumed that the four arrows each represent one of the pillars. It also acts as a reminder that no matter the circumstances, if anyone bearing the mark saw the mark somewhere else, they would all come and band together, to be there for one another.
- "What am I supposed to do? Just tell me what I'm supposed to do."
- "Lean into the best parts of yourself-- your loyalty, your selflessness, your courage, your compassion, and show that side to Emiko. You are living proof that people can change, and you have got to find a way to see that in her, too."
- —Oliver Queen and Tommy Merlyn's ghost[src]
Oliver Queen's vision of Tommy Merlyn inspired him to end the cycle of violence in the Queen family by embracing his best traits: his loyalty, selflessness, courage, and compassion. Oliver credited Team Arrow's success to saving Star City towards their courage, compassion, selflessness, and loyalty, which John Diggle stated to be the four pillars of heroism. Upon Dinah Drake's insistence to symbolize their friendship, Felicity Smoak suggested that she, her husband, John, Roy Harper, Rene Ramirez, and Dinah create a signal to unite them in times of crisis. Oliver dubbed it "the Mark of Four."
In 2040, William Clayton found Roy Harper on Lian Yu and asked him for help, but Roy was hesitant until after digging up Oliver Queen's Green Arrow equipment, Roy found a message hidden inside his bow which had the Mark drawn on it. Roy then proceeded to burn the message and returned to Star City with William.
After reuniting with Dinah Drake, Roy revealed the message to her, which made her question William's intentions for returning to Star City. Soon after questioning Blackstar however, Dinah began to gain trust for William and revealed the origins and meaning of the Mark of Four to him.