Obtained this beautiful vintage jumbo ESP deck with butterfly backs. 10 different symbols, with the 10th looking like an upright slanted 'not equal' mathematical sign, plus 10 more of these 'not equal' cards. Possibly roughed in some manner but hard to tell given their age. 2 large red elaborate butterfly designs on the back of each of the 20 cards. Gold gilded edges on the cards.

ANybody have an idea what the trick was with this unique deck ?

I will describe the face designs again. There are 10 identical cards with a vertical line with two slash marks across it. Then 9 or 10 more cards, each with a different ESP symbol. Anybody know what these cards are for?