What's in a name?
..."I named my spacecraft Sigma Seven. Sigma, a Greek symbol for the sum of the elements of an equation, stands for engineering excellence. That was my goal - engineering excellence. I would not settle for less"...
From: "Schirra's Space", by: Wally Schirra
..."Sigma means "Sum of"..a mathematical term. I wanted to get off the "Gee Whiz" names and use a technical/test pilot term as well as acknowledge the Original 7. I also toyed for awhile with the names Phoenix and Pioneer, but settled on Sigma because the flight was the sum of the efforts and energies of a lot of people"...
Astronaut, Wally Schirra; in "All we did was fly to the moon"
The Real Thing
Sigma 7 was the third and final logo designed and applied by Cece Bibby. She moved to California and was not around to do Gordon Cooper's 'Faith 7'. As with the other logos, most of it was lost during re-entry.
Souvenir
Wally Schirra seemed to be very happy with the Sigma 7 logo. Not only did he wear the souvenir patch, he even signed pictures using the 'E7'.