[meteorite-list] Letters on centimeter cubes?

[Gerald Flaherty]

I've owned a pair of 10 mm cubes but haven't used them in any photos.
I imagine the letters signify the 4 compass directions and top & bottom.
With an oriented FALL in situ, I understand how the cube would be used.
My question is, if photographing a purchased meteorite for the purposes of 
scale ONLY, where orientation is not an obvious factor, is there a preferred 
cube face or is it arbitrary, up to the photographer?
Jerry Flaherty