The seller claimed it was 70 years old, and I think he might be right: this exact printers' block seems to have been used for Paillard ads like this one.
For scale, here it is next to J's discovery: a yellow Victorinox Alox First Mate (Swiss Army Knife with marlinspike).
If you are wondering what the actual Hermes 2000 that this die was modeled on looks like, Richard has one on his site photographed from a remarkably similar angle:
And here is the engraving, a very close mirror image of Richard's picture. Anyone know how best I can get a good print from this? Obviously naively treating it like a rubber stamp is yielding suboptimal results...