This always amazed me: "A Jewish tradition that dates from at least the 19th century is to write plus using a symbol like an inverted T. This practice was adopted into Israeli schools (this practice goes back to at least the 1940s)[11] and is still commonplace today in elementary schools (including secular schools) but in fewer secondary schools.[12] It is also used occasionally in books by religious authors, but most books for adults use the international symbol "+". The usual explanation for this practice is that it avoids the writing of a symbol "+" that looks like a Christian cross.[12]" [1]

[1] http://en.wikipedia.org/wiki/Plus_and_minus_signs#Alternativ...