Do you want to hatch chicks? Even though you don't have a rooster/fertilized eggs, you can obtain them if you want to let them set and hatch - many of us who have roosters in our flocks will sell fertilized hatching eggs, chances are there are people around your area who have eggs readily available.
A broody hen will remain on the nest day and night. If approached she will make noise and may make efforts to defend the nest. Her overall posture is "puffed up". I use a 3 day/night test for my girls to determine that they are serious about being broody - if she stays on that nest behaving broody for that long and I want to hatch that is when I introduce the eggs I want her to set.
If you don't want to hatch chicks or are not set up to accommodate doing so you can "break" the broodiness -- there are several approaches you can read about here on BYC, but my preferred method is the "broody buster cage" which is simply a wire bottomed cage that is set up on blocks to allow air flow from underneat -- the hen, feed and water go in this cage and that is all (no bedding, etc) -- leave her there for a few days and then let her out - if she goes back to the nest and acting broody, back in the cage she goes.
Silkies are generally a breed that is prone to broodiness, so this likely won't be the last time you find yourself dealing with a broody hen. If you aren't depending on them for egg production (a broody hen stops laying) - which, given the breed you likely aren't since they are not a prolific laying breed to begin with - and you aren't bothered by their broodiness you can ride it out by just letting them be broody. It *can* be hard on a hen as she will become inactive and cut back on eating/drinking while she is brooding (she only leaves the nest a couple of times a day to eat, drink and poop) and some hens find the process to be quite draining - so if you aren't actively having them hatch it can be to everyone's benefit to break them.