NSFW is not censorship,nor is it a rating. It definitely is not a political statement.
NSFW stands for Not Safe For Work. Which means you should not open this up when you are at work, because a nude image may pop up at an inappropriate time. An employee or your boss may walk behind you and see it or another image that may not be appropriate for work. And any video which may contain nudity, pornography or profanity.
NSFW is internet slang that went viral on it’s own, like IMHO, LOL, WTF, etc. There are unconfirmed reports it started on Usenet groups in the late 1990s. It seems that NSFW caught on in late 2001 and early 2002. The first definition appeared in 2003 in the Urban Dictionary.
The first generation iPhone was released on June 29, 2007. So NSFW couldn’t possibly have anything to do with apps or Apple policy since they weren’t around in 2003.
Laws against sexual harassment in the workplace are getting strict. A male may have a female co-worker that sits across from him with an open view of his monitor. She may feel harassed by the constant parade of nudity on his monitor and feel it is being done to make her feel uncomfortable, thereby creating a hostile work environment. However right or wrong her conclusion or the judgement of the stray passerby, it is meant to protect the viewer from getting in a sticky situation. A situation that may get them written up or fired. NSFW is meant to protect the viewer by giving them notice that nudity may pop up on the screen that is inappropriate for a workplace environment.
“How do I know if I should mark my work NSFW?”
Ask yourself would viewers (and myself) making personal use of the Internet in a public or formal setting such as in a workplace, school, church, temple or synagogue be violating policies prohibiting (even inadvertent) access to sexually provocative content. Would this put someone’s job in jeopardy?
That is it. It applies to visual content only.
Don't make it something it is not. No high horse or soapbox needed. No revolution or grand diatrbe. Just be courteous to your reader and let them know, "Hey, you might want to check this out at home in private.” Give them information to make their own decision.
Using the NSFW tag is a simple courtesy to your viewer, NOT a requirement.
Also, the term Safe For Work sometimes abbreviated to SFW is used to label material that may have a questionable title or include subjects that could potentially be NSFW but are not.