No-one seemed to know what it was. For quite some time we thought it might be a cover for pests [eg. cockroaches]
In the center of the oval are the words - "ECCE HOMO"
SKULL AND CROSSBONES: A skull and usually two bones crossed, as in this example, were placed on the foot of crosses or on the ground nearby in crucifixion scenes. The legend is that Golgotha, the place of the skull, is where the first man, Adam (Hebrew for "man") was buried. The blood of Christ, the second Adam, saved the first Adam as well as mankind. According to John Chrysostom, Homily on the Word Cemetary, "Mary took the place of Eve; the tree of the Cross took the place of the tree of the knowledge of good and evil; the death of Jesus Christ took the place of that of Adam. Thus was the devil defeated by the very instruments of his victory." Besides the skull and crossbones, crucifixion scenes show the body of Adam (or his skeleton) underneath the cross. Schiller attributes the use of Adam to Romans 5:12-19
and to I Corinthians 15:22-23 (NJB), "Just as all men die in Adam, so will all men be brought to life in Christ." Quenot, 170-71; Schiller, 130-133.
It was also a favorite symbol on Christian graves to show a joyous liberation from the flesh and to serve as a warning to sinners of the vanity and brevity of earthly life."
The symbol itself is quite old, and appears as a funerary symbol in christian catacombs.
In the middle ages, it was a common tombstone decoration, and appeared in many "memento mori," illustrative reminders of mortality."
There is a skull and crossbones image on the tomb of Anne of Cleves in Westminster Abbey.
There is splendid skull and crossbones on a 16th-century gravestone in Durness churchyard in Sutherland,
one on a gravestone in Kirkham in Lancashire, and a skull and crossbones at St Thomasís Church, Lymington, Hampshire.
The carved representation of a Skull and Crossbones at the entrance to some of the old disused churchyards in the City,
is indicative of the burial-place of the early victims of the Great Plague of London. "
Old Cemetery Boston
Once one end has been removed, a drawer can be extracted inside which can be placed treasure, human remains, magic books and spells or any of the smaller monsters.
Any number can be added together to construct walls of crypts."
Note: I've just searched google for 'catacombe case' and reckon they are modern - but I love the last sentence - a wall of crypts !!
But - It still didn't answer the questions about my treasure: