Board Thread:Support Requests - Getting Started/@comment-10569546-20130607210836/@comment-3030984-20130607213748

Well that depends on what wiki you were looking at.

If you were on Uncyclopedia, then yes, they have a content warning when you visit the site that was added by Wikia. I haven't seen it on any other wiki, so it is unlikely that it is available for wikis to request to be enabled. Uncyc has a lot of adult humour, hence the warning.

What you are probably seeing if you are on another wiki is a spoiler warning. This can be added to any wiki using the SpoilerAlert script at Dev Wiki. Just follow the instructions on the page above to add it to your wiki.