A very interesting post by Mario Livio, searching for the origin of the “+” and “-” symbols we find ubiquitous today:
The ancient Greeks expressed addition mostly by juxtaposition, but sporadically used the slash symbol “/” for addition and a semi-elliptical curve for subtraction. In the famous Egyptian Ahmes papyrus, a pair of legs walking forward marked addition, and walking away subtraction. The Hindus, like the Greeks, usually had no mark for addition, except that “yu” was used in the Bakhshali manuscript Arithmetic (which probably dates to the third or fourth century). Towards the end of the fifteenth century, the French mathematician Chuquet (in 1484) and the Italian Pacioli (in 1494) used “” or “p” (indicating plus) for addition and “” or “m” (indicating minus) for subtraction.
There is little doubt that our + sign has its roots in one of the forms of the word “et,” meaning “and” in Latin. The first person who may have used the + sign as an abbreviation for et was the astronomer Nicole d’Oresme (author of The Book of the Sky and the World) at the middle of the fourteenth century. A manuscript from 1417 also has the + symbol (although the downward stroke is not quite vertical) as a descendent of one of the forms of et.
I thought this was an interesting sidenote for “+”:
As a historical curiosity, I should note that even once adopted, not everybody used precisely the same symbol for +. Widman himself introduced it as a Greek cross + (the sign we use today), with the horizontal stroke sometimes a bit longer than the vertical one. Mathematicians such as Recorde, Harriot and Descartes used this form. Others (e.g., Hume, Huygens, and Fermat) used the Latin cross “†,” sometimes placed horizontally, with the crossbar at one end or the other. Finally, a few (e.g., De Hortega, Halley) used the more ornamental form “.”
Speaking of crosses, and doing a bit more research, Wikipedia notes that:
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) and is still commonplace today in elementary schools (including secular schools) but in fewer secondary schools. 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.
+1 for learning more, right?