Most websites consider NSFW to be graphic images only. Text is usually exempt from NSFW tags. I don't know what hubski's opinion on it is, but I'm guessing just the standard "NSFW for images" thing applies.
NSFW was mainly used as a way to alert others that there'll be something immediately noticeable in the workplace, and thus to not click on the link. NSFW text isn't immediately noticeable, and thus okay. Though some users like to use NSFW for text due to wanting to find or avoid that type of content, rather than if it's okay to be seen at work.
As hubski discusses topics (of all kinds), I'd say just use NSFW for images.