What is a "Sooner?"
Originally the word "Sooner" meant a person who had illegally crossed the border of Oklahoma's Unassigned Lands before they were officially opened for white settlement on April 22, 1889. The Sooners who arrived early had the best choice of land and only had to lie low until they could safely emerge and file a claim. They were naturally disliked by the immigrants who entered Oklahoma legally, and in the early days to call someone a Sooner was to attack his character.

By the 1920s, the name lost its negative connotations, and Oklahoma referred to itself as the Sooner State, just as Texas was known as the Lone Star State and Illinois as the Land of Lincoln. "Sooners" swarmed into the old Indian nation and so symbolized Oklahoma's affirmation of a Western heritage.

Also, increasingly, "Sooner" came to be a synonym of Progressivism. The Sooner was an "energetic individual who travels ahead of the human procession." He was prosperous, ambitious, competent, a "can-do" individual. And Oklahoma was the Sooner State, the land of opportunity, enterprise and economic expansion, very much in the Progressive spirit that engulfed the old South in the 1920s.
Also...The Oklahoma Sooners are known as one of the greatest football programs in the nation.

As for the 1918-You will never know, But trust me it means somthing