The signs on the cave come from the Phaistos Disk.
The Phaistos Disc (also spelled Phaistos Disk, Phaestos Disc) is a disk of fired clay from the Minoan palace of Phaistos on the Greek island of Crete, possibly dating to the middle or late Minoan Bronze Age (2nd millennium BC). It is about 15 cm (5.9 in) in diameter and covered on both sides with a spiral of stamped symbols. Its purpose and meaning, and even its original geographical place of manufacture, remain disputed, making it one of the most famous mysteries of archaeology. This unique object is now on display at the archaeological museum of Heraklion.
The disc was discovered in 1908 by the Italian archaeologist Luigi Pernier in the Minoan palace-site of Phaistos, and features 241 tokens, comprising 45 unique signs, which were apparently made by pressing pre-formed hieroglyphic "seals" into a disc of soft clay, in a clockwise sequence spiraling towards the disc's center.