What cause Adult warning on your site?
if you don't want to have an adult disclaimer before people are viewing your site, your should not use terms that imply an adult nature of your site, like "sex", "porn", "nude" etc.
Generally, very explicit words but more so explicit pictures and videos cause sites to be marked as adult. The rule of thumb is that bare breasts are not allowed and poses shouldn't be too sexy with almost no clothes on.
Note that site and user names pointing to illegal pornography (like underage, animals or bestiality) will be shut down no matter what content is on those sites.
