1929: Hanna Citation from Charles Lindbergh

Hanna and Charles Lindbergh
In the late 1920's the Union Pacific Coal Company in Hanna painted the building name on the roof of each of their buildings and mines. The name was painted in all capital letters. Why did they do that? The answer is provided below.
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Lindbergh (Union Pacific Coal Company Employe's Magazine Volume 6, Number 3, March 1929)