I know that this may not help those looking for submissive women in a public place, but it might for those looking to see if the ones they are already with are.

It has been my experience that in the bedroom, and especially during sex, that I can tell if she is submissive. I think this has something to do with all the barriers coming down during an intimate act. All the walls, masks, and acting drops and you can truly see them for their true desires. I have found three of my past lovers were submissive this way. Two of which during the day were ones that you would not think were submissive.

What to look for?
If, like a dance, she lets you lead the sex.
If she looks at your pleasure first to her own.

Just my thoughts...