Yeah all that is true, but not all silkies have such obvious signs. There is alot of genetic factors that change those things. I have a silkie line that has so little comb/wattles, that most hens have bigger comb/wattles than my rooster. Also the streamers can show up at 3 months old, or 6 months old. So before 6 months old, you can only hope for an obvious sign.
You can tell by posture, by the long legs........by the streamers, by the look of the tail, by the shape of the chest. But alot of signs are so subtle, that you have to get used to them by raising them. I had 3 roosters that got to 5 months old and you finally saw some streamers to know they were boys. Sometimes the signs are quite obvious, but if you want it to be a pullet bad enough, you convince yourself you do not see them LOL.