TD Ameritrade planted an ASCII flag – that is to say, imprinted an advertisement – on bitcoin's blockchain earlier this month.
The online broker announced that it sent 68 bitcoin transactions to create a digital flag with its logo on the bitcoin blockchain, in a post published this past weekend.
The company used the OP_Return feature in bitcoin's protocol to insert the characters, creating 68 invalid transactions as a result. Due to the nature of the blockchain, this flag is now forever preserved on the cryptocurrency's ledger.
"We love finding new ways to use emerging technology. So we decided to have a little fun and plant our flag. Okay – technically, we embedded it," the broker said, adding:
"With a part of the blockchain called OP_Return, which functions like the memo space on a check, simple messages and characters can be placed within transactions on the blockchain. By linking 68 individual transactions, with 80 characters per transaction, we were able to create the larger image."
No bitcoins were actually transferred through these transactions, according to data from Blockchain.info.
OP_Return was first introduced in 2013 as a way for users to include some messages in the blockchain. However, the Bitcoin Core 0.9 release notably stated that developers were not endorsing data storage in the blockchain, saying that "storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere."
The official bitcoin wiki page notes that OP_Return can be used to convey information.
"We're proud to be part of it. Forever," the broker wrote.
TD Ameritrade image via Jonathan Weiss / Shutterstock