What specific characteristics do you consider to show strong & attractive masculinity?

Confidence is the main thing definitely. A confident man doesn't need to "act like a man" and he doesn't need a woman who "acts like a woman should" in order for him to feel more like a man. To me thats the main thing, just be you and happy, and that works for men and women just the same. Have the confidence to be yourself and as a man it will appeal to women, and same for vice versa.