To sign the letter "F" in American Sign Language (ASL), you can hold up your dominant hand with your palm facing out, and touch your index finger and thumb together while holding your other three fingers up and spread apart. Make sure to form a circle with your thumb and index finger touching, otherwise, if you flatten out your thumb and index a bit more, it will look like you are signing the number 9. You can use this sign to finger-spell simple words or the initials of objects, places, animals, or peoples names.

There are also video resources available on YouTube that demonstrate how to sign the letter "F" in ASL.