I think this is the most likely origin of the word: >Another theory "suggests a source in Yiddish kikel "circle." Accordingly, Jewish immigrants, ignorant of writing with the Latin alphabet, signed their entry forms with a circle, eschewing the customary "X" as a sign of Christianity. On this theory, Ellis Island immigration inspectors began calling such people kikels, and the term shortened as it passed into general use." https://en.metapedia.org/wiki/Kike https://www.etymonline.com/word/kike