It looks like Zack Snyder's Justice League accidentally uses an Halo icon.
As PCGamesN reported over the weekend, the Deathstroke character has a symbol on his sword that appears to be a Halo emblem.
The symbol was spotted on Deathstroke's costume by actor Geoff Reeves, who visited the #SnyderCut Exhibit in Dallas, Texas recently. At the time, this symbol was taken to refer to the famous Batman villain, Ra's Al Ghul.
