Now there is a MATE emoji starting from the 4th beta of 13.2 version of iOS. It is not about our desktop environment, though. The emoji represents the South American beverage MATE takes its name from.
Hope it arrives to Android soon!
Not unless we claim our MATE first, mwaha... 
Just kidding, it doesn't quite work like that, since emoji's are graphics of the Unicode character - which appears to be already available for me -->🧉
:mate: is a custom emoji for this site, :ubuntu_mate: too. I wonder how that'll pan out when Discourse gets the emoji's updated to the latest spec.