Overall, the effect is a negative resistance at the emitter terminal.

To alleviate this, the second transistor often has a resistor of a few hundred ohms connected between its base and emitter terminals.

In this circuit the emitter terminal of the transistor serves as the input, the collector the output, and the base is connected to ground, or "common", hence its name.

A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals.

So, even if we couldn't read the part number on the transistor, we now know what the device is, what it's pinout is and that it has a diode connected across it's collector and emitter terminals.