This page tests whether a meta tag with a name of "rating" and a content of "mature" is respected.
If you are seeing this page, your current setup does not block content labelled in this way.
The <meta name="rating" content="mature"> tag is sometimes used by adult websites to mark themselves as such. While this seems to imply a lower age rating that the "adult" one, it does get used on sites that host content which would be considered adult in most places. It seems safest to me to just treat the two to be equivalent.