A stock symbol is a shorthand code, usually 1 to 5 uppercase letters (though it may occasionally include a dot), which represents a company with respect to a stock exchange such as the NYSE or Nasdaq.
... - Graham Hill, (United Kingdom)
1965 - Graham Hill, (United Kingdom)
1966 - Jackie Stewart[?], (United Kingdom)
1967 - Denny Hulme[?], (New Zealand)
1968 - Graham Hill, ...