The recent discussion* of the rules for determining the sign of the product of two signed numbers suggested a study of the ways in which this question has been treated in algebras in the past. A problem of this type does not merit an exhaustive investigation. The question is how have various authors gone about the task of making this rule reasonable to the reader. The volumes chosen for the study were simply those that happened to be at hand: several of them were very influential; others were perhaps a bit obscure.