I can shed a little insight into this type Calso sign. This appears to date from the 1930's -1940's.
In the 1930's, Standard of California expanded eastward into Standard of Indiana territory, using the "Calso" name, derived from the name "The California Company". To set itself apart, Calso adopted lime green, white and blue instead of Standard's red, white and blue.
Apparently, after WWII, Standard of California decided to rebrand all its Calso stations in the Plains and Rockies to Chevron, and set up Calso (as the "California Oil Company" in the Mid-Atlantic and Northeast states, with a new logo design: the word "Calso" on a red background, with an elongated "L". The Chevron logo was eventually introduced on the East Coast by the mid-1950's, but both "old" and "new" Calsos would become "Chevron" by the 1960's.
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