The person charged with translating 字典.词典, being familiar with online sites called “dict.” may have written that down on a piece of paper and given it to the sign painter, who misread the final “t” as “k”. That’s not so far-fetched as it may seem, since Chinese cursive styles sometimes write “t” in a way that might be confused with “k”. It’s common to see “s” being mistaken for “p” and “l” for “t”, or “G” being mistaken for “J”.