Most cards are oriented vertically, with the text reading from left to right along the shorter (2½") side of the standard card. For all the examples in this post, the card is "flipped" over it's right edge.
I consider the "correct" orientation to be like this:
|Photo swiped from Nick at Dime Boxes|
Looks like the grading companies agree. A quick search appears to show that they encase cards in this direction too. If you turn it to read the grading label, the right side is against the label at the top.
The backs of horizontal cards may be vertical and can reveal if the designers agreed with this arrangement.
|In this case, they did.|
Now the really strange part is, vertical cards with horizontal backs are actually the opposite, in the sense that the back rotates clockwise 90° or "Left Side Up".
This seems consistent through more modern sets.
So horizontal fronts with vertical backs go counter clockwise, and vertical fronts with horizontal backs go clockwise.
But not always....
I've found some examples that diverge from the "norm". There are a few sets where all the horizontals are Left Side Up throughout the whole set. And there are others where it just plain gets weird.
1994 Score has all horizontal backs. To keep all the backs in the same direction, the horizontal cards end up Left Side Up. I omitted the arrows because you probably get the idea.
Well OK, that's all fine and good. At least the whole set is like that.
There is (at least) one Topps flagship set where things seem to have gone awry.
1997 Topps has a couple sections of Prospects cards. They are horizontal on the front. The backs are vertical. For some reason, the orientation flips around among these. There could be others, I haven't verified. Check it out:
|Backs are all the same. But flip them all over at once....|
|Whiskey Tango Foxtrot Topps??|
And the most bizarre design I've come across so far is 1993 Select. These have sort of a two-tone green frame design on the front that varies between left and right facing, as well as horizontals too. But it really goes nuts when you find that some of the vertical cards have horizontal backs, and some of the horizontal cards have vertical backs. It's really just totally random.
|Left front frame - vertical back|
|Right front frame - vertical back|
|Vertical front - Horizontal back!|
|Horizontal front and back|
|Horizontal front - Vertical back|
So the bottom line question is really this - Which one of these below is "Correct" to you?
Let me know in the comments. Then go enjoy your properly socialized lives.