BS”D
Shygetz Aross actually comes from Jewish market traders in Spain. When rice with an insect problem was found, they would mark it “Sheketz Arroz” (arroz is rice in Spanish and sheketz is of course an unclean creature) in Hebrew characters so that they would know not to sell it to Jews. Later, the phrase was used to mean that an unwanted guest, such as a thief or moiser, was entering the market, and it was shouted at such characters to warn them to leave before the traders would repel him in the manner known today as “Chaptz’em”.
An unscrupulous trader named Nebela or de Menubal, an ancestor of the Admou”r meCreedmoor, would write “Sheketz Arroz” on all of his competitor’s schoire, thereby rendering it unfit for sale to Jews as kasher lemehadrin. Generations later, after the Inquisition, the phrase made its way into Yiddish, and eventually, the forgotten phrase was revived by the first Schmoigerman (the European version of the name came from adding Shoiteh and Gas Ruach to the original Menubal surname, turning it into roshei teivois SH oiteh M enuval V e G as R uach), and then adding the -man suffix to be able to register it in the Austro-Hungarian Empire) to serve as a Chassidish rebbe, Rabbi Lemach Kenaan Schmoigerman, whose sefer “Machloikes Rishoinim” listed it as a segula for keeping machloikes alive.