What's this black rectangle painted on the side of a V-1 flying bomb?
A &quot;Pallung&quot; is a piece of wood (or something similar) that prevents ships (or something similar) from falling over when they are on land. &quot;abstellen&quot; means to put something down (such as luggage) or into storage. There are some recent articles that contain the word &quot;Pallung&quot; on google news, such as this one.
Assuming that the book depicted in this pdf is authentic, you can see what an Abstellpallung for a V1 looks like on page 29, indicated by the letters b and c:

Note that the text twice says &quot;Markierung am Rumpf beachten!&quot; (mind the markings on the fuselage), which probably corresponds to the black rectangles mentioned by the OP.

(Some native German users have indicated that they have never heard the word. Neither have I, until today. I am not sure about other languages, but in German, some domains have very specific vocabulary that a layman will almost never get in contact with. One example of this is anything connected with ships, another one is hunting, and there are probably some more. The manual contains another example just in the preceding sections (what does &quot;heißen&quot; mean here?). So &quot;I have never heard the word&quot; may just mean that someone is not familiar with some particular domain.)