Yes any Polish x would have a crest and it would start showing up early, by 3 weeks they would have a nice crest going on.From the barred rock X babies.. only the boys will be barred like this.
THIS IS what black sex link boys from RIRxBR look like. Females would be solid black.
Polish crosses *should* have a bit of a crest.. as cresting is a dominant feature.. according to my current understanding.
Gender is a bit harder on the Polish and any crosses. But by 4 weeks wattles should be showing if a boy. And by 8 weeks should be sure. My only caveat to this is with a Polish x Silkie. I thought mine was a girl until at 11 weeks she crowed everyone was saying girl and I was saying boy just from his behaviour.
I do like a nice barred rock and wattles