I had a student once manage to start a C150 with the key in upside down. It started but the starter switch stuck in the start position. The only obvious indication to me was the starter warning light. I suspect, if it was my hand on the key switch, I would have noticed something amiss that a low hour student may not.
The requirement was in CAP747 (GR no. 1) but I now think it is an EASA requirement.
It is relatively easy to take a wire from the output of the starter solenoid to light the warning light when there is 14V at the starter.