I've put some of my Google-fu to work, and unearthed various sites. First, a post
in the EXETOOLS forum, with the tool used to strip the executables from the RICH information. It seems the original information about the signature was posted at wasm.ru, but of course, it's in Russian. The first post there includes some file, and the tool comes with a machine translated version (Russian -> English) of the original RTF file that came with the tool.
Second, in the documentation
of a library used to play music in XM format, and co-authored by the same guy (at least with the same screen name) of the above tool, I found this:
There's another MS linker-specific known issue. link.exe attaches some unnecessary data between DOS stub and the beginning of PE header. It's easy to spot the dead weight in a Hex editor - it begins with a magic word 'Rich'. The encoded machine compid follows the magic word. If you don't want your executables being signed this way or just don't like to spend some extra bytes (actually, it's half a Kb!) on the signature, there's a couple of workarounds available. First, you can switch to another linker. Or you can search the web to find an article on patching link.exe. Psst! It's written in russian and available somewhere at wasm.ru.
Finally, in another forum, an attachment
(do not worry, it's a pure text file), the most interesting document, and one that throws quite some light over what's the purpose of the RICH section. Still, it does not clarifies what's exactly stored there, only makes some suppositions.