Probably very little of this is true
but there is some background information that is historically accurate: for centuries, Jamaica was one of our most important trading partners. We would send them our salted cod, and they would send us rum. That's why salt fish is a staple in most traditional Jamaican cuisine, and why rum is synonymous with Newfoundland. That part is definitely true.
In the past, all rum was called screech here. Today, that's a specific brand name for just one type of rum. The story behind that is supposedly an American general was in St. John's and heard a man yelling, and said, "Who is making that Godawful screech?" and came the reply, "Screech? T'is the rum, me son!" And that's how people started calling it Screech. Obviously, likely untrue.
The other likely untrue part is that the fishermen would kiss their cod at the docks before it was sent south to Jamaica, from the sheer joy of knowing it would come back to them in the form of rum.
So that's the background. The ceremony is only for CFAs (Come-From-Aways, our word for any visitor not from here). They're gathered together - either in a pub, or at a wedding, or in a private home, wherever. They've given a little history lesson about Newfoundland and some of our "greatest accomplishments" (little trivia bits, basically - we invented the gas mask, had soldiers fighting with Abraham Lincoln, first responded to Titanic's distress call, yadda yadda).
Then they have to go through a few rituals intended to delight to crowd of locals watching. They'll have a bite of Newfie steak (bologna or Vienna sausages), a shot of Screech rum, and they have to kiss a cod. Then they have to recite a few lines in Newfoundland English. The Captain screeching them in usually plays this part up.
"Shortest conversation in Newfoundland? Arn s'marn? N'arn! Now, arn s'marn means "Are there any fish this morning", and N'arn means what?"
- "None?"
"No, it means, no there are not any fish this morning. Now, "hey b'y" is Newfoundland for "I agree", not to be confused with "Yes b'y", which has 1,000 different meanings. So if a Newfoundlander says something to ya and you don't understand it, sure just say "Hey b'y", because you don't want to make him repeat, he's only going to say it the same way. So then, your next phrase is how ya gettin' on me ol' cock and long may yer big jib draw!"
(Silence, until one of the CFAs catches on and says, "Hey b'y!" and everyone cheers).
On and on that goes.
Then they get certificates from the Royal Order of Screechers that name them honourary Newfoundlanders. It's a silly little tradition, really, but wildly popular.