As far as most BDSM is concerned, dress is dress, and neither necessarily mean anything.
There are, however, many commonalities.
At a party or gathering, for example, a collar is usually indicative of an owned submissive- that is, a submissive that is controlled by a Dom(me). Some use Dom(me) because it can be male, Dom, or female, Domme.
This is not always the case, as some just like wearing the collars for other reasons.
Most of the time, a Domme will wear more elaborate or nicer clothing- a corset, leather/PVC, fishnets or stockings, etc., whereas a female submissive sometimes wears some basic leather or PVC, but mostly little or no clothing- but chains, rope, collar, etc.
Doms often wear leather or more elaborate clothing, and sometimes just regular pants and shirt.
I hope others have input on this, as tha more you know, the better!