Dutch Windmill Code?

Windmill Code Used by Dutch Resistance?

Windmills are part of the Dutch landscape. According to Wikipedia, the positions of sails of Dutch windmills were "used to signal the local region during Nazi operations in World War II, such as searches for Jews." If this text (present from the first version of 2 March 2023) was taken from Goleta Valley Historical Society) (present as early as in August 2022), the paragraph break in the latter suggests that the signalling was made by one specific position of the sails. If so, the information conveyed would have been no more than an on/off alarm.
According to Traces of War, the windmill Vrijheid in Beesd "was used in World War II by the resistance to sent messages by the position of the wings. To commemorate this, the hitherto unnamed mill was named "The Freedom (De Vrijheid)" after the renovation in 1968." According to machine translation of the explanation board, the position of the sails was indeed used to pass on information, and the name "de Vrijheid" was given in commemoration of the efforts to regain freedom during the war, but the connection between the passing of information and war-time efforts is not clear. But Wikipedia confirms "During World War II, the mill was used to send signals to the Dutch resistance. This was done by the position that the sails were set at."

Traditional Meaning of Windmill Positions at Rest

At least, it seems certain that the position of the sails of a windmill at rest has been traditionally used to convey some meaning, though there is discrepancy among sources about the specific meaning. According to one source, a position slightly tilted to the left means joy; a position slightly tilted to the right means mourning; a straight position like "+" means a short rest (no operation for a few days); a diagonal position like "x" means a long rest (no operation for weeks), etc. (Olie Molen de Passiebloem). The same image (reproduced below) is posted on many websites (Google).
This form of expression was actually used in some public occasions. Windmills were placed in "mourning position" when many Dutch people were killed in a Malaysian aircraft shot down in 2014 (CNN quoted in Wikipedia) as well as when Prince Friso died in 2013 because of a skiing accident (PresReader, wind mill sign language in Holland).

Long Distance Communication like Optical Telegraphy

Regarding communication more than a simple expression of some meaning, apart from Wikipedia, the magazine Popular Mechanics (June 1908), p.365 (Google) reports the Dutch government's experiment to use windmill signaling for military purposes between mills some miles distant. It says secret code had been used "from generation to generation of millers." (The idea is similar to the optical telegraphy known from the eighteenth century.)

Use by German Agents?

According to Cathleen Small, Code Breakers and Spies of World War II (Google), p.13, during the First World War, German agents used starts/stops of the sails of Dutch windmills to transmit messages in Morse code.