Le mercredi 11 avril 2018 14:19:18 UTC+2, a écritÂ*:
In many countries it's just a personal choice and decision, no registry involved. In such countries, if in a particular competition two sailplanes bear the same marks, the Competition Director will ask one of them to change his ID. As a CD in Italy, I might ask to the pilot with a shorter career to perform the change in "respect of the longer career", or I might ask the competitor who in my opinion has the easiest option to change his ID (i.e: AI can very easily be modified to AT, AF, AE etc.) to oblige. Or I may apply any other ideas in my "best" judgment.

In other countries (the UK and probably others), the national federation is responsible for keeping a registry of compID's.

Sporting rules for competitions usually prescribe that a competition ID (1-3 characters) must be clearly visible on both sides of the vertical fin. This should also be complemented with even larger characters under one wing.. So, check the rules in your country and those of the countries where you will fly (maybe France and Germany for example), so that you do the work properly, once and for all.

If painted, in some countries a popular choice is to replicate the last 2 characters of the registration marking, so if you sell your glider, the compID may simply continue with the new owner (i.e: D-KABC - "BC").
Other pilots have such strong ties with their ID that they'll use the same for all their career (think Giorgio Galetto, forever "Y").

Aldo Cernezzi
www.voloavela.it

In Germany, there is an official registration with the DAec - but most do just as they like. In the scenario described by Aldo, the one who is not registered will be asked to do the change for the during of the competition by some lengths of tape.