In fairness to Lithuanians, they can see the difference between Poles and Lithuanians due to different names and languages.

On the other hand, Poles of Belarus are indistinguishable from Belarusians having the same Slavic names speaking Belarusian or Russian languages. Poles of Belarus don’t speak Polish at all. Only on rare occasions such as Catholic churches.  The only way to know if a person is a Pole if he or she acknowledges his or her ancestry.