Here's a concrete suggestion: the Bing search engine and IE browser
support this safe flag right now. Could you talk to the people
responsible for them and ask whether they considered more fine grained
schemes such as PICS, and why they implemented a single bit instead?
Or, I can go to their website and see that their “bit" implements ternary
logic:
Bing implements the exact proposal in this I-D. (The I-D says so.)
If you believe otherwise, please provide references.
R's,
John