Can you tell a Russian from Ukrainian? Can you even tell an Ukrainian name from Russian name?
rus. Volk ~ ukr. Vovk
rus. Aleksey ~ ukr. Oleksiy
Different suffixes: rus. Tarasov ~ ukr. Tarasenko, Tarasiuk
Ukrainian surnames often have no suffixes at all (more often than in Russia): rus. Melnikov vs. ukr. Melnyk
rus. Kovalev vs. ukr. Koval
Although it doesn't say anything about a person's nationality for certain because of migrations.Different cultures, different languages, it's obvious to the locals.