The comb. It's very large for the age of the chick (You didn't mention the age, but I'm guessing about three weeks by the size of the box) and in comparison to the others. I have had terrible luck with silkies, with every single one I've ever gotten turning out to be boys, so i have kind of gotten the hang of it. I would also make note of their behaviors. Some males might show signs of flock leadership early on. A couple of mine would call the other chicks to roost at night from just a few weeks old, were dominant with the other chicks, etc. You certainly cannot go by behavior alone, but it might help get you looking in the right direction for possible males. Watch for large combs and long, pointed saddle feathers, and an upright stance. You can look for streamers off the back of the crest, but is difficult to recognize true head streamers before their head fluff is completely in.Thanks for the info! Can you tell me how you were able to make your prediction (so I know for next time). Thank you in advance!