Ahh I mean from the watch itself yes... nothing to do with Ant pairings..
Each device does have a unique unit ID (for example, you can view it in the UI under the Settings->System->About on the 920), but I don't believe that Connect IQ currently has a way to retrieve this. Out of curiosity, do you have an example of how you would use this information? I'd like to submit this as a suggestion, but it would help to provide a use case in my submission.
In your submission consider that an id should be available from the fit file once fit is implemented. Just in case this avoids some potential doubling up.