The Comb: Usually, a male will have a larger comb than a female. Also, a Silkie cockerel's comb seems to develop faster than a Silkie pullet's comb. However, some males will have very small combs and some females will have very large ones!
The Crest: A Silkie cockerel's crest will be shaped differently that the Silkie pullet's crest. The male's crest should show "little streamers" coming from the back of the crest. It looks a bit "swept back." and not really round. The pullet's crest should be nicely round in shape without the tell-tale streamers.
The Wattles: Generally, a Silkie male will have larger and rounder wattles than a Silkie female. However, this trait is a bit easier to use for sexing with non-bearded Silkies. With top quality bearded Silkies, the wattles of both genders are nearly non-existent and even the males frequently show very small wattles.
The Spurs: Silkie cockerels will usually have them and the females usually won't.
The Sounds: Silkie cockerels crow. Silkie females usually don't BUT hens have been known to crow...
The Eggs: Silkie pullets should eventually lay eggs. However, there are cases of cockerel-looking Silkies that lay. I would say that this case is rather unusual and laying eggs is the best indicator that your Silkie is a female!
The Feathers: Silkie cockerels will develop "male feathers" on their hackles and saddles. (For those folks in doubt about terminology, the hackle feathers are the ones on the neck and the saddle feathers are the ones just in front of the tail.) These male hackle and saddle feathers are longer and more pointed at the tips than the feathers on the Silkie pullet's hackle or her feathers in front of her tail. On Silkie cockerels, these saddle feathers may even tend to lay over the wings a bit.
The Tail: Silkie females typically have rounder and softer tails than the males. Silkie males usually show a more pointed tail because of the presence of "normal" or "hard" feathers in their tails. Keep in mind, however, that although the Standard allows some "hard" feathers in the Silkie cockerel's tail, in top show quality males, hard feathering in the tail is discouraged and often is not present. In creating a perfect "show" Silkies, the ideal for both male and female is a perfectly round and wide tail so this trait may not be as helpful in sexing Silkies as some others.
Here are a few funny stories... I know of a very reputable and honest master Silkie breeder that sold a pair of Splash Silkies to a newcomer to the breed. Unfortunately, to the dismay of the master breeder both turned out to be cockerels! It wasn't until the second male was nearly a year old before he developed proper male characteristics. The breeder was very embarrassed to be caught making such a mistake.
Valerie Hirvela sent me a mystery bird last summer. It was a non-bearded Black Silkie "something." The "mystery bird" was a year old and had some pullet features and some cockerel features. She guessed "it" was cockerel but couldn't tell for sure. I changed my mind 3 times over the next 6 months before deciding it was a cockerel. HE finally started crowing. In the same box was a non-bearded Black pullet and she had to go broody before I was convinced she was a SHE!
Frequently, in front of the cages where Silkies are exhibited at poultry shows, Silkie breeders openly debate where a particular bird is a cockerel or a pullet! In fact, I'd be willing to bet that with no other breed of bantam is THAT particular issue contested right among the show cages by experienced breeders!
Many, if not all, of the tips listed above require comparing males to females so I'm not sure how much the novice will be helped by these words. With sexing Silkies, the case is not so much "practice makes perfect" as practice tends to lend a better successful percentage. I guess sexing Silkies is a subtle thing. So many breeders tend to refer to a "feeling" that the particular Silkie is one gender or the other. By the time that my Silkie chicks are 8 to 12 weeks old, I can usually guess about half of the Silkie's genders right. Of the other half, I am as likely to get it wrong as right. All in all, it is slightly better than a coin flip. At three or four months old, I usually band my Silkie chicks. At this point, I'll make some notes on what I think I've got. A couple months later, I'll try again and compare my results. Still, I'm constantly surprising myself or perhaps I should say that those Silkies are constantly surprising me!!!