Here are some quotes from Coke’s website…

Keeping tabs on a favorite…

TaB was The Coca-Cola Company’s first sugar-free drink, introduced in 1963, when 28 percent of Americans had begun watching their weight. Its name was a play on the notion of people keeping “tabs” on their weight.

Although sales of TaB were surpassed by the introduction of diet Coke®, the brand still has fiercely loyal fans who have been known to travel hundreds of miles to find their favorite drink. (link)

-and-

This sugar free drink, launched in 1963, was one of the first ways consumers cold keep “tabs” on their diet. TaB was the Coca-Cola Company’s first sugar free drink and se the stage for the wave of diet colas that followed. Today, the pink can is still a distinctive statement. TaB has achieved pop-culture status and has the reputation of being somewhat hard to find. If your grocery carries TaB, drink up and enjoy your good fortune! (link)