When people not from Newfoundland (aka "Mainlanders") visit Newfoundland, it's a common tradition to get "screeched in"

The person will first take a shot of Newfoundland Screech (a type of rum) and then kisses a fish (usually a cod) in order to become an official honourary Newfoundlander.

A few ideas for the stamp design:

-A fish next to a bottle/shot glass

-Someone kissing a fish

-The certificate some places fill out and give to people who were screeched in

(Photos were just taken off of Google Images as a reference)