so how was this introduced to reddit, it was not on the front page for long if ever. if not for reading here I doubt I would have ever encountered it
They also have a blog post  about it.
> The button is a feature that the popular social media site Reddit introduced on April 1, 2015. It has its own subreddit at /r/thebutton.
After April 1st it hasn't been that visible though
It was also most likely featured at some point on trending subs. And if you read a hell of a lot of reddit, you'll see it mentioned elsewhere on the site (like in memes, comments etc)