I am sorry for putting up a rather trivial question (this is literally a shower thought), but I am wondering if any of his own writings or somewhere else mention this. I realize that the vast majority of what he was looking at was either not acceptable or very boring, but I'd like to know if there was a patent for something revolutionary, important or famous, idea of which was stamped with Einstein's approval.
I have not heard of anything like what you are asking, but there are a lot of indications that the kinds of inventions he was involved in overseeing did influence his thinking on relativity. One of the major categories of invention at that particular time were attempts to synchronize clocks over vast distances, for example, using electrical signals — a serious problem to European rail industries, where lack of proper time coordination not only could lead to incorrect schedules but also to accidents. The similarity between many of these patents and Einstein's own clock-coordination thought experiments has been discussed by several historians of physics, notably Peter Galison.
See, e.g., Peter Galison, Einstein's Clocks, Poincaré's Maps: Empires of Time (Norton, 2003).