You're confusing PICS with ICRA.
PICS is merely a framework that is implemented with a policy definition language. ICRA is the one with the gazillion tags that uses the PICS framework.
Go to this page, create a label, they need an email address, so, make sure you have one that doesn't bounce. With that email, they send you an RDF file that includes your definitions.
http://www.icra.org/label/generator/
Then, in each page of HTML put:
<link rel="meta" href="http://domain.com/labels.rdf" type="application/rdf+xml" title="ICRA labels" />
<meta name="rating" content="restricted">
If you have access to setting mod_headers, the following will tag ANY file requested from your site -- graphics, videos, etc even if they are hotlinked.
http://www.icra.org/systemspecification/
If you don't want to go through the pain of defining your own ICRA tags, I have attached labels.txt. Edit the one location that says domain.com and rename it labels.rdf and put it at the root of your website.
With those two changes, I believe that you can honestly say that you have made a best effort attempt to clearly label your sites as adult content.
It works now, its probably supported by the search engines, it is supported by the safesearch tools today. Pretty much a done issue.
Now we just have to get the word out.