UN Stamps recently has launched the Ethereum-based UN Crypto Stamp.
Each stamp bears a unique secret code hidden behind a scratch-off area. The secret code enables its owner to activate exactly one counterpart of that stamp on the blockchain as a digital collectible.
The creation, ownership, exchange and trading of the digital stamps is managed through a smart contract deployed on the Ethereum blockchain.
The availability is limited to 90,000 stamps in total, 30,000 per issuing office (Geneva, New York, Vienna), and encoded into the smart contract.