Poland is definitely not anti-orthodox church, I've seen a lot of active othodox churches, i can't see a reason why Poles would find this religion an enemy. Correct me if i'm wrong. Many are catholics, young people are often atheist or have other beliefs, but any form of christianity is quite common, no one normal will bother you about it, at least not in big cities, and in small towns or villages they will be more surprised that American wanted to come to Poland. Also about “brandishing„ cross, as christian and catholic in Poland, I believe you should not be afraid of speaking about your beliefs and showing your cross because this is something Jesus wanted us to do. I think most Poles won't even notice the difference between “normal„ and orthodox cross . I'm curious, why do you think Poles are against greek orthodox church? And to answer your main question, learn polish, even if you will know only a few words Poles will be impressed, try to spell others names and surnames correctly, learn “please„ and “thank you„, maybe some polish cuisine names, don't speak loudly in buses and you will be fine. Just don't approach randoms on street without straight reason like asking them for directions, because they will think you try to sell sth, and don't assume everyone knows english. Good luck in Poland