That is actually an official translation of the Danish word: gækkebrev.
Sometimes people have to remind you about a tradition, that you actually learned at a very early age. A gækkebrev is a letter, where you cut pattens into a folded paper with a scissor - then you add a riddle to it, and you only reveal your name with dots: Janet would be .... The receiver is to guess who sent the letter, a false guess will generate a chocolate Easter egg for the sender, a correct guess will be prized with a chocolate Easter egg for the receiver. Nowadays it is only children who eagerly remember the tradition - they want their chocolate eggs :o)
On my humble attempt I would have written the ridded in the outer ring of my letter and then enclosed a fresh snow drop (the latter is optional as not every Dane has access to one).
The gækkebrev originates in the old "bindebrev" - if you received such a letter on your nameday, it contained either a riddle or a string with nots, that needed to be untied. If you could not solve it, you were to throw a party.
These days you are able to find cutting instructions for a gækkebrev in most Danish women's magaizine when snowdrops start to appear sometime before Easter. This pattern is from "Hendes Verden " No 7 2005, and you are quickly reminded that only thin paper works when cutting a gækkebrev.