I found this impressively large two inch long cockroach just like this, sticking out its abdomen from the side of a creek bank after dark. I found the behavior odd, and I suspected that it might be releasing pheromones to attract a mate. I really had no idea if cockroaches did that or not. After some recent reading, that does appear to be part of the courtship ritual. To initiate courtship, a female will call nearby males in this manner. Presumably then, this is a female.
A while later, I managed to catch her in a different pose.