Giving a blowjob is already a sexual act that requires the woman to be submissive. Of course it gives her more power over you than you might think (remember the guy who married his wife because of her oral skills), but in general “going down” is a submissive gesture.
If she then also swallows your cum, which implicates an even more submissive gesture, you can confidently assume that she sees you as her leader, her lover and her man.