The World Scout Bureau has issued a JOTA Participant Card for every year except the very first JOTA held in 1958. These are not really QSL cards. They were sent out after each year's JOTA to those members of a group who submitted a JOTA report to the World Bureau on their JOTA experiences (along with a list of participants). Thus they are kind of in a category by themselves. Since they arrived well after the JOTA, they typically weren't postally used, but simply served as a souvenir of their JOTA participation.
These cards had that year’s JOTA logo & a blank box where the participant could write their name, with "Took Part" printed below the box. The Participation Cards for all the years can be seen (but only in black & white) in a book published by World Scouting in 1993 called The JOTA Story - 36 Years of Scouting’s Worldwide Jamboree-on-the-Air, 1958-1993 by Len Jarrett.
Here is the complete JOTA Participation Card collection for you to see and enjoy. This collection was partially compiled by the Scouts of China Radio Team and copied with their permission.