"Not Safe For Work".
Browsing the Interweb from work can be a risky business. If you are caught looking at something that appears to break the company's usage rules you can find yourself getting fired.
Images and links that could, even mistakenly, be seen to break these rules should be marked 'NSFW' to ensure people at work know not to click it.
The links board has a NSFW setting built-in.
"Link it you prick! If my boss sees that on my screen I'll be in P45 country!"