Superluminal signal velocity is widely assumed to confront Einstein causality and thus the Special Theory of Relativity (STR). Actually, there is only the tunneling mechanism known to permit superluminal signal velocities at present. The demonstrated negative group velocity experiments don't represent superluminal signal velocities. In those experiments only the signal's peak traveled faster than light and the signal was reshaped. In this Note we shall discuss why tunneling allows superluminal signal velocities. However, opposed to text books on STR we have shown that a superluminal signal beam does not allow the design of a time machine.