Just for the heck of it, I decided to add some code to the Comic Template that lets you add the issue's rating to the page.
Now, you can add the "| Rating =" field (new pages should have it already) and input "T", "M", "T+", or "E" to indicate the rating that is listed on the cover of every issue, in accordance with DC's recent addition of a ratings system. The system was only introduced in 2011, so not every issue will have it.
Adding the rating will add the issue to the category "Issues Rated T" (and M, and E, respectively), and Comics by Rating.
I don't expect anyone to get a huge kick out of that, but if you weren't expecting to see boobs or F-bombs in an issue you read, then you probably missed that it was Rated M.