RUSH rewards are given to users who have connected certain game accounts to the Player Rush site. These rewards are given for a few different actions those players perform in those games.
To gain RUSH rewards by playing Rainbow Six Siege you must first connect your Rainbow Six Siege account to Player Rush. To see how to do that please check out our article on Connecting Rainbow Six Siege and Player Rush.
Once you have connected your account you can visit your Rainbow Six Siege Dashboard.
There you will see your stats and rewards for Rainbow Six Siege, as well as the Player Rush Rainbow Six Siege Leaderboard. Player Rush members gain RUSH Rewards for all kills made in Rainbow Six Siege.