Well actually, yes, there is a proposal, to be published as part of
the Boston W3C workshop on resource discovery, RSN.
The idea is to do (from memory):
<meta name="robots" content="noindex">
A more complete spec will be available of course :-)
Of the big services at least Lycos, WebCrawler, Infoseek and Excite
have indicated they want to support this.
At WebCrawler we will support this RSN; I put the code in last week,
but it is not yet deployed.
-- Martijn
Email: m.koster@webcrawler.com
WWW: http://info.webcrawler.com/mak/mak.html