It appears my user manual is up to date and working. (not sure if I would say properly)
I searched Badges and the link leonieDF provided did not come up.
Search Badge and it does. (sheesh)
That is if you search the version of the user manual from the Aperture Help menu. If you search the Aperture Help manual from the web based version (http://documentation.apple.com/en/aperture/) both searches will provide the Understanding Badge Overlays links. (bigger sheesh)
This is why Aperture is considered more of a Pro application. If you're looking for something in a Pro application User Manual, you either need to be very specific when you search, or make sure you search the correct version of the same manual. It's best if you not only know exactly what you're looking for, but where it actually is in the manual. Better still, a Pro doesn't need a User Manual at all. They buy the software, figure out how it works, including all the cool undocumented stuff and write their own user manual. Then they come here and help all the non-Pros.
For non-Pro applications, you can search badgers and it knows you're really trying to understand the definition and use of the term Badge and it will give you each and every possible reference and/or variation of the word Badge. (badge, badges, badging, badged, badge-a-lot, etc.)
Frank should have written the user manual. Then you could search bdges and all the necessary links would come up. Much more helpful.
Sent Apple feedback on adding a glossary and improving their User Manual search algorithm. That should fix things.
(if you haven't guessed, most of this post is supposed to be funny)