I notice biting around the eyes. Aggressive pursuit of specific females even in tanks with multiple rays. Some males "bounce" up and down rapidly, sometimes while biting the disc. When there is consistent aggression between M/F usually leads to breeding.
Just be careful, I've seen females who weren't willing to breed die due to over aggression from courting males. respected keeper Jim Barry lost a nice Male from a barb stab during breeding that punctured something vital, the female got defensive.
I clip the barbs on some females for this reason now