When there is an “X” present in a bitcoin addressA bitcoin address is a unique cryptographic key that “owns... More, that is an OP_RETURN script, which is a way to add a message to a BTC transaction. OP_RETURN is a script opcode used to mark a transaction output as invalid. Since any outputs with OP_RETURN are probably unspendable, OP_RETURN outputs can be used to burn bitcoins. Many members of the BitcoinThe term "Bitcoin" can either refer to Bitcoin the network, ... More community frown on the use of OP_RETURN, in part because Bitcoin was intended to provide a record for financial transactions, not a record for arbitrary data. That being said, OP_RETURN can be used for digital asset proof-of-ownership, and has at times been used to convey additional information needed to send transactions.