If you are looking to mark little chicks, I use the Vet Wrap (from the feed stores) for birth to about 2 weeks old. They have lots of colors, you CAN write on them with a black sharpie, and they stretch as they grow. After 2 weeks I go to colored zip ties, put on just tight enough they can't get their feet out. With silkies I put it above their 5th toe so it doesn't come off, but really loose. When they get big enough I decide who I want to keep, that's when I put on their numbered poultry leg bands.
I bought mine from a show - but you can get them online easily. A quick search turned up tons on Ebay, as well as online poultry supply companies.
http://compare.ebay.com/like/251258620206?var=lv<yp=AllFixedPriceItemTypes&var=sbar
For Silkies I would suggest 9 or larger - give them room for their feathers too.
P.S. - I don't think anybody can ID chicks.. they have to be quite a bit older... preferably 6 months