In baseball scoring, a backwards "K" symbolizes the batter striking out looking. A regular "K" is used for strikeouts in which batter swung and missed for the third strike.
Because not all typefaces include a backwards "K", some styles opt for the nomenclature "Kc" for a strikeout looking; this stands for "called strikeout" and is contrasted with "Ks" for swinging strikeout.
The use of "K" for strikeout was necessary because the letter "S" was being used to signify sacrifice. Additionally, the abbreviation "SO" stands for shutout. The "S" abbreviation for sacrifice is rarely used as of 2014; instead, "S" is used for saves, whereas sacrifices are marked as "sac" for sacrifice bunts and "SF" for sacrifice flies.