From GameWatcher: “Rainbow Six Siege is no stranger to odd bugs, but did you know that you can crash the game with emoticons? We were as surprised as you might now be, rest assured. That is, you could do so, though Ubisoft did patch that one up just recently.
The catch is, however, that you can get banned for exploiting the chat symbols, and it would seem that Ubisoft will be dishing out bans of varying lengths according to the severity of each player’s exploitation of the said bug.”
Source: N4G PC You can crash Rainbow Six Siege by exploiting emoticons