Does anyone know of the existence of a deck of number cards that comes ready marked on the back (1-9)? The markings would have to be secret markings.

My feeling is that we might use this to our advantage when using mathematical procedures such as 'casting out the nines'.

If none exist then I guess the plan B would be to edge mark a deck of 'Uno' cards, but this would be more problematic to the eye with respect to discernment.

No luck it seems? It surprises me that there is no such deck already in existence.

Fortunately something has come on to my radar that may well fit the bill (as well as being suitable for a number of other devious purposes).The cards in question come with a wonderful new effect called "Symbiosis".

Paul Brook had a double blank Svengali deck. I wanted to use this years ago having multiple mathematical problems on them.
The spectator writes a random number and selects a card. You immediately solve the problem. So, for example you are great at multiplication of 11 or getting the squats root, then that is your force card.