Marks do not have to be unique. It is the act of doing so, symbolised by the mark, that forms the contract. It was commonly just an X. This particular case hin

Marks do not have to be unique. It is the act of doing so, symbolised by the mark, that forms the contract. It was commonly just an X. This particular case hinges more on whether the emoji :thumb_up means agreement or acknowledgement. However if the person had habitually been agreeing with a mark then that would weigh in favor. It's not clear without the exhibit of previous text messages, but strongly implied by the wording, that this was indeed the case. So this was accepted as a written contract with mutually agreed terms. There was no verbal addendum or additional terms.