DO NOT use magazine or book art scans except for personal use.
Can I make a suggestion? Go to daz3d.com and download all of their free software NOW before it isn't free any more. (They'll start charging again on May 1.) Then you'll have a character with poseable hands and you can create your own renders of signs.
I'm very familiar with Daz studio, so I'll help you a litte if you like.
Once you have your own art you are free to do what you want with it. It also means you can do things like look at the signs from different angles, etc.
In fact, you can create animations and show the sentence structure that way instead of just single pictures.
Let me know if you are interested in this. I find it interesting.
EDIT: Found a technical article that is more detailed than you need, but it shows the kind of posing I'm talking about. What you'd be doing is MUCH simpler than this. I think you may be able to buy ASL poses ready made. I'll look for them.
DAZ Pose Control Tutorial
EDIT 2: Yep, here is the ASL alphabet.
Aiko4 and V4 Hand It Over
EDIT 3: Here is a free pack with letters and basic signs (animated.)
American Sign Language Vol 1
I believe they can, but you should contact the author to make sure the poses can be used for commercial purposes.