A marked deck is one where a card can be identified, or partly identified, without seeing its face. Custom decks manage this by accident all the time.

The orientable back

If the back has a top and a bottom — a logo the right way up, a word, a scene, a border that is thicker along one edge — then a card that has been turned round is visibly different from one that has not.

In most games that is harmless. In any game where cards get rotated, or where somebody is paying attention, it is information leaking off the back of the card.

The drifting cut

Cutting has a real tolerance, roughly a millimetre either way. If your back design runs a thin border close to the edge, some cards in the run will show a white sliver on one side and others will not.

That is a mark, and it is one you paid for. The answer is a wider border, or a pattern that bleeds off all four edges so there is no reference line to drift against.

The single-card giveaway

Anything unique on one card — a promotional message on the ace, a different back on the jokers — is fine as long as it is on the face. On the back it identifies that card from across the table.

How to test yours in two minutes

Print the back at size, twice. Rotate one. Put them side by side and look at them from a metre away.

Then print twenty and cut them by hand slightly off-register. If the edge changes tell you anything, widen the border before you commit to the run.