Devil's work?

The Kingdom of Bavaria in southern Germany was part of the federal German Empire from 1871. Bavaria remained autonomous in many areas. The Bavarian kings of the House of Wittelsbach retained their own army and postal service and also issued their own stamps bearing the state name Bayern (as early as November 1, 1849!). This lasted until 1918, when King Ludwig III was deposed and driven out by a popular uprising. In March 1911, King Ludwig III's predecessor, Prince Regent Luitpold, celebrated his 90th birthday, and a series of 16 stamps was issued on the occasion. On the low values, he is depicted with a beard, and on the high values, dressed in hunting attire. The designer was Prof. Friedrich August von KaulbachHe was apparently no friend of the monarch, for the high-value stamps, which he adorned with laurel wreaths, included heads of mocking devils everywhere! The printer of the stamps, the Topographical Institute of the Ministry of War, noticed nothing. They printed little devils laughing at the monarch and even sticking out their tongues at Luitpold! The designer had clearly included his initials on the low-value stamps, but he certainly did not dare to do so on the high-value ones. The initials FAK are incorporated very faintly and small in the stamp image. In June 1911, the Professor was given another chance to play a trick on the monarch. He designed two stamps to commemorate the 25th anniversary of Luitpold's regency. Here, too, he incorporated little mocking devils into the wreath surrounding the portrait of his sovereign. It was not until much later that the mocking devils were discovered, but by then the Kingdom of Bavaria no longer existed. And Luitpold himself probably never knew about it either, as he died in Munich on December 12, 1912. He was succeeded by Ludwig III. Are there any other stamps in existence in which the designer included these kinds of jokes? I am curious!