[nic n dave]

i hatched my own chicks a while back and 3 hens went to my sister, i hadnt seen them since i gave them to her and at 17 weeks of age i went to see them, i gave her 2 silkies one black one white and an exchequer leghorn. i didnt sex these bird myself someone did it for me, well anyway ive gone down to her coop and my goodness the black silkie its huge!! at least double the size of the white silkie in hight and width! the comb looks slightly different but theres not much in it, could this be a cockerel, this particular black silkie was hand raised by me at a few days old as mummy hen starting attacking her. we all hoped it would be a hen as we got attached to it being in our home

[joyfull]

Silkies are one of the hardest to sex and often you cant tell until they either lay or crow I'm afraid 

[rileyfin]

Look above the beak, if the flesh is lumpy and quite large and, depending on age, has a tinge of plum/burgandy rather than black this is a sign the bird is a cockerel. Also the head feathers will be more elvis like rather than very round, with long thin spikey feathers rather than fluffy ones.
I had one hatchling last year who was huge, I thought it must be a boy but she is a girl and a very loving one at that. Boys even at a young age I have always found to be quite cagey, where as the girls dont mind a bit of lovin 
Hope this helps

[Abacus]

Its easy enough to get them wrong! I had one weedy looking rescued specimen who I was convinced was a hen and six months later 'she' has graduated from Clementine to Basil and is this magnificent cockerel parading around the hen run trying to convince himself he is in charge...

[Axe]

what about the card test?...if you check the feathers where the head meets the neck, put the card against the neck and lift up slightly so the feathers rest on the card...check them..if they have a pointy tip then its a cockerel...if they are rounded then its a hen.
http://msucares.com/poultry/management/poultry_sexing.html

but the easiest way is to see if it lays an egg lol

[joyfull]

silkies don't have feathers like other chickens (they don't have the barbs to keep them together in the feather shape and so look more like they have fur rather than feathers) so not sure this would work.

[GrannieAnnie]

My 2 white silkie hens were much smaller than my other ones, but I realise that's not a lot of help.  Like Joy said, silkies are notoriously hard to sex.