Well written and scientifically plausible - a rare gem.
The problem with a lot of the early Superman stories is that they relied heavily on sci-fi aspects, but often the science was bad. Not so with 'The Stolen Superman Signal'! This story is based around the superman signal device that Jimmy Olsen has concealed in his wristwatch - a device that can emit a high frequency ultrasound only Superman can hear (yes, this concept was later used in Superman the Movie). When describing the device, they get it right, and even include a plausible diagram of the watch in a close up panel. Granted, signal watches were already all the rage in Dick Tracy comics, and it may not be the most exciting or high-tech gadget ever shown in a Superman comic - but it sure is a refreshing change!