The chest feathers will give you the best indicator. Soonest to come in, and dark/ black ones mean male. Our male SF also developed a pink comb quite early too. Girls remain lighter....although poor quality SF can have darker feathers, they won't be black.
I'd assume pullet, but I usually waited on mine until they were at least two weeks to make any concrete sexing decisions. I also knew how my line feathered out. So many Salmon Faverolles have very inconsistent feathering patterns with females much darker than they should be.