Setting a rule for NPF

["Rocky Hotas" <rockyhotas%post.com@localhost>]

Hello!
I am a newbye with NPF, but it was suggested to me few months ago in this mailing list as a good instrument.
I would like to simply log the reception of ICMP packets (in a single network interface): should I simply use a rule? Following "man npf.conf" I found that the syntax could be like

rule "test" add pass proto icmp

But how can I specify the logging action?
I didn't found with Google any useful example of an already written rule and so I don't know how to proceed.
Bye!

Rocky