I have left the card blank but the supporting book clearly describes ideas on how to adorn your blank card. the deck is "The Quest Tarot". I have not done anything on mine and I do not use it.....yet......After discussions here I can see where it might be used.

Ahhh kind of like an extra card then? I always wonder about the self adorned cards, they do seem to fall differently when coloured and have a different weight so I can pick them out and then I wonder if I was influenced by that?  Perhaps try in a deck but keep it blank and decide on the meaning before using it?

I have been investigating the blank cards.....
Nearly all packs will come with two extra cards, mostly because the sets are printed in multiples of tens so they have to print 80 cards to get 78, a bit illusion shattering that, bit like the extra blank pages at the back of some books, but most decks use the extra two for advertising or telling about the deck and I like to use one top and bottom to protect my cards. Leaving them blank is a relatively new and interesting idea I think and not many decks do.

Would be interesting to get others to look at their decks and see what they find?