I'm have a low cost (<2$) soldering iron, similar to the one shown in the image, except that it has 3 plug terminals.
Suddenly something got me thinking about safety, out of curiosity I cut the wires, to find only 2 wires (I was expecting 3). I was wondering why I'm not getting a shock? I touched the metal heating rods and tips, nothing happened (with a tester first, of course). I don't find any isolation between the heating element and me. I'm guessing the neutral is wired on the outer side (which should be very close to ground potential).
The overall circuitry is just a diode and an led with 100k series resistor.