Amina wrote a nice post.
at the age you're looking at, there aren't going to be hackle or saddle feathers. Comb size and color is going to be your red flag, along with color and possibly leg thickness. Any bird with red to the comb, I'd avoid. Pullests should have minimal size to the comb at this age, and it should be fleshy colored, not pink or red. Patched of different color--red, silver or gold, just different than the main body color--on the shoulders/wings is a male sign, but 4 weeks might be too young to see this. Thicker legs are usually a cockerel trait, as is a bold attitude.
I'd say spend some time looking at pea comb pictures here. At this young age, the triple row is a pretty good indicator of a male. Females will have a single row of bumps, males will have a main, larger row with smaller rows on each side.
If in doubt, post some pics here and we can guide you.