At 6 weeks, most single comb American breeds can be sexed very, very accurately by the comb and wattles. The pullets just stay yellow-ish until closer to maturity. The cockerels sprout them red and large at 6-7 weeks. You can rarely miss it at that age. It won't be much longer and you'll know.
Watch the combs and wattles. Those are the visuals.
Sometimes, really experienced folks detect a "stance" difference, with the cockerels being more likely to be "head's up" and standing erect. This is a rooster's instinct when keeping watch in a flock and sometimes the little cockerels demonstrate some of these qualities.
Thicker legs are often another sign, but one needs a known pullet standing nearby to see the difference some times.
Anyhow, that's it. Stick with the comb and wattles. If they sprout over the next three weeks, red and protruding? Yup. That's a cockerel.