My wife has a few collars. Daycollar has some that are collars but dont really let most people know they are collars. As with everyone else i think its meaning is how you define it. To me my wife's collar is a symbol of not just her being my wife but by wearing it she says to me that she is happy to be my submissive. She is choosing to give herself to me. I treat her like a precious treasure but i will admit i consider her my property. In all fairness she is allowed to consider me her property also in that we are monogamous and we literally belong to each other. We figured in order for one to "belong" to the other there has to be an air of property right. That doesnt mean i dictate her every move or treat her as less than human. It means for us that one is owned by the other and cannot be had by anyone else, much like your house is your house and people arent allowed to squat there.
She doesnt always wear her collar, its usually reserved for special days when she wants something subtle to scream, "I'm yours, i serve you!" This works better for us because it makes her wearing it even more significant. Something used often will occasionally become meaningless, sometimes when something is reserved and savored it is held more meaningfully. Only the two of you can really define what that means between you.