Adding a subkey notation

[Marko Božiković]

Hi,

I've looked for a way to add some sort of comments on subkeys - I'd like to
have multiple authentication subkeys and easily distinguish among them.

>From what I've read, notations seem to be the way to go, but I was unable to
find a way to set them on already existing subkeys...

In general, I haven't found a comprihensive documentation on notations
anywhere. Is there some kind of guide/best practices documentation for them?

Thank you,
-- 
Marko