I was contacted by a collector about this yesterday and told him what I knew then: that it is an old 6 of Hearts on the back of which is written, in apparently archaic French, a description of a Roman coin. I didn't know which coin, but a little subsequent digging suggests a minor bronze piece of Constantine II, "CONTSTANTINE IUN.", S3850, the reverse of which contains the words VIRTUS EXERCIT, and two captives seated at foot of trophy "deux captifs asses aux cotes d'un standart".
We can be absolutely certain that it is not card money!