One-half:
Here is a more "casual" way to sign 1/2
Note: In everyday usage, most fractions are often done while holding the hand palm
back with the fingertips pointing somewhat to the left.
One-fourth:
For all of the various fractions you just show the numerator, then move the hand down a bit and show the denominator.
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars