I don’t speak Russian. But there are a few sounds when I overhear conversations that tip me off the speaker is speaking Russian- like “pozhu” and “byeh”- actually a lot of the “soft” vowels in Russian. This is just from observation; I have no background in phonetics or Slavic language study or anything like that, so I may be totally wrong.
This is also the way I recognize Korean. If it sounds a little like Japanese, but I don’t recognize any of the words or grammar, it’s Korean. I’m still working on a “half-ass standard” for distinguishing between Chinese dialects. My friend says “if it sounds like someone nagging you or cursing you out, it’s Cantonese.”