The Ruby Play Button is given to YouTubers for reaching 50 million subscribers.
It is in the shape of the YouTubers icon and is a red, transparent colour.
So far, only two channels have been given to the Ruby Play Button, PewDiePie, who reached 50 million subscribers in December 2016. and T-Series, who reached 50 million subscribers in June 2018. (however it has not been revealed or delivered yet.) Play Button was given to the first YouTuber to reach a subscriber milestone immediately after reaching it. The Ruby Play Button is also the first YouTube Play Button to not be displayed and or distributed during a VidCon event.
YouTubers who have the Ruby Play Button
PewDiePie's Bro Fist Ruby Play Button