[Nottingham] uname decoding

[Penfold Q]

I've been looking for a couple of days now and haven't found a
satisfactory answer in the man pages, info pages or google so I thought
I'd ask if anyone here knows...

On a linux host, `uname -v` starts with a # character and a number. What
does this signify?

This is not present on Mac OS X, Solaris or HP-UX (maybe others) and so
the man pages, etc don't explain it, they just explain the meanings of
the options, not the output.

Anyone got a clue?

-Penfold