What document indicates the legal ownership of a financial security and entitles the holder to payments?

The document that indicates the legal ownership of a financial security and entitles the holder to payments is best represented by a bond. A bond is a type of debt security that is issued by entities such as corporations or governments to raise capital. When an investor purchases a bond, they are essentially lending money to the issuer in exchange for periodic interest payments and the return of the bond's face value at maturity.

A bond serves as proof of the ownership of that security, detailing the terms of the loan, including the interest rate (or coupon rate), maturity date, and payment schedule. The bond itself signifies entitlement to receive future cash flows, making it the most accurate choice in this context.

While a coupon, which is typically a part of a bond that signifies the interest payment, is indeed related to payments, it does not itself denote ownership of the security. Instead, it is the bond that encompasses ownership rights and payment entitlements.