One thing I often look at when I see a woman in bondage is whether she is wearing a collar. To me it is sign she is submissive and is accepting of his (or in some cases another woman's) control over her.
Photo is courtesy of www.bondagemaidens.com
In my novel Praxton the women not only wore collars but it was expected that they be locked. I believe a locked collar is a reminder to the woman wearing it she is dependent on her Master for the amount of freedom she has.
The collar can be used or worn a number of different ways. First, it can be hidden where the woman can wear in public, for example under a turtle neck. It can also be disguised to a degree; a choker looks a lot like a collar and to a wearer it may mean the same thing but to others it looks like a necklace.
A collar can also be of varying widths and wider styles(sometimes referred to as posture collars) can restrict the head movement. Rings attached to the collar also allow for additional bondage. One can attach by a short chain wrist cuffs to the collar that greatly reduces movement. Or the Master can attach a leash to the collar. The collar with a leash by itself is a sign of complete control over her.
Take a look at some of the online stores offering collars. There are both metal and leather ones available with varying degrees of quality and design. Matching cuffs can also be bought to compliment the collar.
Explore a little at the different sites offering bondage equipment and accessories. The women are likely to find more than one kind they find attractive and enjoy wearing them.