AD Ameritrade stored forever an AD on the Bitcoin Blockchain, using the OP_RETURN command and spending 68 transactions. You can watch the full AD on their website https://www.tdameritrade.com/blockchain

They create a digital flag with its logo on the Bitcoin Blockchain creating 68 invalid transactions and the AD Flag is stored forever on the cryptocurrency’s ledger. OP_RETURN is a command introduced to include messages in the blockchain.

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