My Word is My Bond ?

This is a common English phrase, used in other languages too, and means that whatever I say or consent to, can be trusted. So, what is the history and how relevant is it in today’s digital age?
We must not confuse this phrase with identity verification ‘per se’. Whilst the two are closely related, the verification of an identity does not imply consent or a signature. However, a signature must be linked to the person that signs, for it to be meaningful or legally valid to any degree. So how did “My Word is My Bond” first be a valid phrase?