One of the most common descriptive notes people have to write using text when they post links or images to blogs, comments or anywhere in HTML is to say \"this link is not safe for work\" or simply \"NSFW\". By adding the <NSFW> tag, this could be made much simpler and standardized. Browsers could then have an option to automatically hide all <NSFW> content. A tag is preferred to an attribute since it could then also be used around content and not just links. 

Examples:

<nsfw><a href=\"http://www.example.com\">Pics here!</a></nsfw>
<nsfw><img src=\"badkitten.jpg\"></nsfw>