My word is my bond: “Dictum Meum Pactum!”
Meaning, that by just giving my word you can be assured that the promise of action I have just made will be kept.
Originating from the London Stock Exchange since the early 1800s where financial bargains and trades were made with no written pledges, no documents, and no contracts. Reputation was collateral in 19th Century England. Trust was built up and your bank of trust guaranteed you trading opportunities.