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IME the older Escher labels, with the 4 men, are stuck on there hard. Usually leave residue if they wear off. Almost impossible to remove in routine honing. OTOH, the later labels with & Sohn and 2...

First pic def looks thuri ...... the size is one that Escher made many stones in. If it has diagonal saw cuts in the sides, maybe a rough hewn look on the back .... that would indicate an Escher....