It is not always as simple as you might think to identify what bird a feather comes from, but in the case of hawk feathers, it's typically relatively easy. If nothing else, hawk feathers can usually be distinguished from those of other birds by their size as well as their coloring, and by the fact that hawks in certain regions are typically very distinctive.

As a general matter, if you live in an area populated largely by one type of hawk, it will eventually grow to be second nature for you to identify that species' feather, thus making it simple to eliminate the possibility of a particular feather belonging to the local hawks or to some other type of bird.
Of course, if you aren't familiar with a particular hawk or species of hawk, you may still need help to identify hawk feathers. The following are some basic features you should learn about hawk feathers to aid you in quick, simple, and accurate identification.
In most cases, a hawk feather will be larger than basic bird species' feathers, but not as large as, say, the feathers of an eagle or a turkey or a vulture.
Some hawk feathers also have very distinctive markings and colorings that are different from those of other birds.
Finally, the location of the feather can give you some clues as to whether or not you are dealing with a hawk feather or not.
All it takes it one positive identification of a feather and you can use it as a benchmark for future identifications until, eventually, all the hawk species in your area are familiar and easy to determine.
If you are still not sure if you've found a hawk feather or not, looking at some pictures might help. You may be able to buy books containing details on different bird feather species, or check in an encyclopedia. You can also look at these hawk images on Foto Search.com for assistance in determining just what a hawk feather looks like.