For starters, a stock ticker symbol is a combination of
letters used to reference a particular stock. A symbol is usually one to four
letters, but can be five letters, says CNBC breaking news producer Peter
Schacknow,but only for specific reasons. For example, Comcast, NBCUniversal's parent company, trades as CMCSA (the 5th letter refers to "class A" shares). Numbers are not allowed to be used in a U.S. stock's ticker symbol.