Amusing post in the "try to make too much of everything" vein. The subreddit header has something on it I've not seen before: "YOU ARE NOT A MEMBER OF THIS CO

Amusing post in the "try to make too much of everything" vein. The subreddit header has something on it I've not seen before: "YOU ARE NOT A MEMBER OF THIS COMMUNITY. PLEASE RESPECT THAT BY NOT DOWNVOTING." I've joined a ton of subreddits in the past (and left quite a few), and I've never seen this before. How widespread is this practice? Does it work?