And sometimes people add those (or other) comments to specify to their own scripts where to begin and end parsing for their own private search engines or indexers. I know that's what I use them for. They're less obtrusive and more mysterious that way :)
That's an old Infoseek tag. It may still be used on sites that use Infoseek's engine for on site search. You can use it to control what sections of the page that the Infoseek engine indexes - like you could have it skip indexing banner codes for example.
Infoseek.com - the web site no longer exists, but the engine, Ultraseek is still out here. Inktomi bought the software, it's now called Inktomi Enterprise Server and you'll find it running on a lot of sites for Enterprise Search. It's also used at www.infoseek.co.jp