The letter of commitment does not need to be thumbprinted. After the promise is signed by the promisor, the promise has become legally effective, and the promisor does not need to press the fingerprint on the promise.
A letter of commitment is a letter of commitment signed by the promisee after making some promises, so that the promisee can confirm the promise. After the promisor signs, it means that the contents of the letter of commitment have been confirmed, and there is no need to press the fingerprint.