I don't think I've ever seen an account with an NSFW tag/flair. Posts? Yeah. Subreddits? Yup. Possibly a flair for your user on a particular subreddit added by a mod for some reason? Sure. But not accounts. Can you link to this tag?
https://www.reddit.com/r/help/comments/pfpw4y/any_way_to_rem...
This link has pictures in it, showing you the NSFW tag:
https://www.reddit.com/r/techsupport/comments/8qhay9/why_is_...
(I don't have any experience with these accounts myself. But I've stumbled across more than one in mainstream subreddits, and my curiosity was piqued. Only pointing this out to note that this comment reflects the totality of my knowledge on the subject.)