My earliest piece of Ido-themed postal history dates from 1908, the year after the language's introduction, but I also have several pieces from the 1960s and 1970s and even a philatelic card with commemorative cancellations from an Ido convention in Germany in 1990. Although Ido never enjoyed a level of success comparable to Esperanto, there are still hundreds of active Ido speakers. There are even Ido and Volapük Wikipedias.https://io.wikipedia.org/wiki/Frontispicohttps://vo.wikipedia.org/wiki/Cifapad
Returning to the topic at hand but remaining in the realm of lingvoj internaciaj
, here's a postcard from my collection depicting an Esperanto airship. The caption translates to "Ever forward! Ever higher!" (if you ignore the typo in the third word).
Here's another, but not from my own collection.