Hidden in plain sight is the genius of Paul Gerber.
He designed the dial with 'PuristS' graphics running left-to-right and vice versa, upright and upside-down such that the capital 'P' and 'S' are adjacent.
This makes the secret double D or kidney shape symbology amongst the Art Deco design.
The secret is the extra tall 'T' that nobody sees.
Regards,
MTF