I picked up this little tool somewhere along the line. I thought it would make a useful probe.
Out of curiousity, I googled it and was directed to the Classic Rotary Phones Forum. Turns out it's for removing the fingerwheel/dial from a rotary telephone, and also for removing the "totalizer" from a coin-operated phone. There were four versions of this tool, and the L3 is apparently the least common. Old technology!
I actually have several working rotary dial phones in my home, so if I ever have to remove their dials I guess I'll have to figure out how to use it.