here's more info on the one with the point down
"The priority sign will be made of sheet metal in the shape of an equilateral triangle with one point down. Each side will be 12 inches long; the corners will be rounded to a 1/2 inch radius. Refer to figure 9."
http://www.m38a1.com/Resources/color_markings.htm
(the above expert is not from this link)
better link that works.