I only have subjective reasons for this thinking and it is not based on any kind of science or long term experience. However, Spotty is non aggressive. He/she shares the burrow, at times, with my Yellow Watchman goby and is not really that aggressive towards the other fish.
To me the males have grumpier, meaner looking faces that are more angular and sharp, which could be attributed to having bigger mouths and further extending maxillae towards the posterior for the mouth brooding duties they perform. The females in contrast have a softer, more pleasing look with rounder features to their maxilla.
Like I said this is just an observation from combing photographs on the web and in books.
Lorraine is in a unique position because she has a positive ID on the male as is evidenced by it's flashing behavior. I'd like to ask Lorraine if she notices a difference in the facial structure between her two BSJF?