If you're traveling to the U.S. with a visa, the U.S. Department of State advises keeping it with your passport. You'll need to present the documents together to customs officials once you arrive. It not only provides personal details about you, your visa has its own unique identification number.
Visa Numbers Are Printed in Red
Your visa number, also known as a visa foil number, is usually located on the lower right-hand corner of your visa. It is printed in red and is eight characters long. Most U.S. visas contain only numbers. However, some may begin with a letter followed by numbers. Visa numbers do not include special characters, such as a period, asterisk or dash symbol. In a few instances, such as with older visas, a visa number can also reside at the top center of the document or have a length other than eight characters.