One of the first questions I ask a Dominant is how they prefer to be addressed. I honestly don't bother with what they call me. They can call me whatever the bloody heck they like.

However, if it's important to you, perhaps discussion of what the terms mean to the two (or three, or four, or...) of you. It's been my experience that almost everyone has at least a slightly different definition of what it means to be a slave or submissive. Perhaps you could consider using it as a "getting to know you" question over that first meeting cup of coffee or bringing it up during contract/ scene negotiation.

(immature note: this is my 69th post! *wiggle*)