"I need your signature."
Translation:Mi bezonas vian subskribon.
Underwriting is something quite different in English! It's a legal/financial term meaning you accept liability in a financial transaction, and agree to pay money if a loss occurs. (For example, if you underwrite someone's mortgage, and then they default on the mortgage, you will pay instead). It's usually used in big financial transactions. But I'm guessing it's from a similar word-root - people having to sign at the bottom of a document, therefore 'writing under' the contract.