It's on the song "Not Alike", and the words are actually said by Royce Da 5'9, rather than Eminem.
Though it was just a very short mention, it's still significant knowing Eminem is one of the biggest names(if not the biggest) in the rap scene or hip-hop music in general.
It's certainly becoming more mainstream, with references to Bitcoin and crypto popping up more and more in popular culture.
Still, I like this song better:
88N8 Digital Gold (https://www.youtube.com/watch?v=4Yu6dA603uw)