The bitcoin network has been running since early 2009, but what is the oldest physical artifact related to bitcoin?
I don't mean computer hardware that was used to run bitcoin, unless it is designed specifically for bitcoin use (ASICs, hardware wallets, etc).
I think paper wallets are an obvious answer as one of the oldest physical artifacts, but those are something best kept private. So more interestingly, what is the oldest 'public' sort of artifact? Material from an early conference? Casascius coins? Something else?