Str82u - 5:20 am on Mar 15, 2013 (gmt 0)
From GWT "Fetch as Googlebot" or cached pages you're looking in the source for anything your site didn't add.
How this can identify the hacking of the site
Probably not for adult content but you should check the reputation and other factors of the reverse lookup you used. Many are using a simple script to highlight domains that contain adult terms but they may not actually be terms a person would read in a phrase (sorry for the lack of examples but you know you can find words in other words, right? Same principle).
if something is wrong with my site then Google will send some kind of warning in webmaster tools i guess
EDIT: Actually, here's a "Nerds" example: If you owned the domain for a resort named "The Hotel Coral Essex", a reverse lookup might pick up terms or words like "hot", "oral" and "sex" then flag the domain.