To Decoy, or Not to Decoy
Some turkey hunters swear by their decoys. There are countless stories about how a decoy made the difference when trying to coax a gobbler into a setup.
The realism of today’s decoys is especially effective, and since most decoys are quiet, easy to transport and set up, many hunters carry one or more in their hunting vests.
Decoys can be particularly helpful when guiding youth, first-time hunters or people with disabilities as they can take the turkey’s attention off the caller.
However, there are times when decoys are less than effective, and they can even spook heavily hunted birds. Hunters must decide for themselves whether or not to use decoys, but if they do, here are some safety rules hunters should always follow.

Proper Use Of Decoys
Unless the use of decoys is prohibited by law, the following guidelines apply:

[ol][*]A decoy should never be visible while being transported. Never carry an uncovered (identifiable) decoy any distance.[*]Always set-up against a tree that is wider than your shoulders and taller than your head.[*]Establish a clear line of vision for at least 100 yards and then set your decoy(s) approximately 20 yards from your position at a right angle to the line.[*]Should you see another hunter (especially if he/she is close to your “line of sight”) call out to them in a loud, clear voice. Their presence has already compromised your location and a “soft” call may only confuse them, rather than alerting them to your presence.[*]If you are calling over decoys and then elect to move to a new location, check carefully to ensure that no one is stalking your decoys. Check before leaving your “stand” tree. Should you see someone in the area, rule 4 applies.[/ol]
I found this on the following website: http://www.nwtf.org/SpringTips/contents/decoy.html