Which of the following describes the nine-digit routing number security feature of a check?

The nine-digit routing number security feature of a check is best described by the use of magnetic ink character recognition (MICR) numbers. This technology allows the routing number, along with the account and check number, to be printed on the bottom of checks in a special ink that is readable by machines, facilitating automated processing by banks. The use of magnetic ink provides an additional layer of security and accuracy in identifying financial institutions and accounts during the check-clearing process.

Other options might include visual or physical attributes of checks, but they do not specifically pertain to the routing number's functionality. Magnetic ink character recognition is integral because it ensures that the routing number can be captured and processed efficiently by banking systems, hence, its designation as a security feature.