According to
this video, Google uses META tags (keywords/descriptions I assume) to filter out sites from Safe Search, since many adult sites don't have any labels indicating the type of content on the page.
So instead of:
<link rel="meta" href="http://www.xyz.com/labels.rdf">
try:
<meta name="keywords" content="free porn, xxx anal sex, blowjob girls, nude babes">
<meta name="description" content="get your gagging bitches here.">