Okay, so you know the basic sign for week is this:
A variation of the sign that is good to know is the "double index" version.
The movement is the same as the main variation above, but in this version both hands are in "index finger" shapes.
The dominant hand slides forward along the side of the base hand to the tip of the base hand index finger.
Note: the sign WEEK can incorporate a number.
For example you can sign "THREE WEEKS" by sliding a "3" across the palm.
This works for numbers 1 - 9. After that you use a separate sign for the number and WEEK.
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars