Rolex Daytona: What is the meaning of the Greek letter “Sigma” placed outside the Ts?

This is an important question between the collectos of Daytona:

What is the meaning of the Greek letter “Sigma” placed outside the Ts?

Sigma is a conventional sign among the various dial-makers and the watch manufacturers, indicating that the hour-markers or the dial plate (and thus also the hands) are in precious metal.

You can find more information in the book Rolex Daytona Story