How do I see what algorithm is used for a signature

[Doug Barton]

I refreshed my key tonight in preparation for a key signing party and 
came across this message:

gpg: Note: signatures using the MD5 algorithm are rejected

I'm sure there is a way to determine what algorithm a signature was 
created with, but the mechanism wasn't obvious to me on an (admittedly 
cursory) exam of the docs.

Not urgent, but if someone has the answer handy ...  :)

Doug