Waving to say Hi or Hello seems to be close enough to universal at this point. It's not completely universal, since there are some cultures, like the Sentinelese that might be isolated enough that they would not understand what it means, but for the most part, you can go most places in the world, wave at someone, and reasonably expect it to be interpreted as a greeting (whether greeting a stranger is appropriate in the culture is another thing entirely).
Various noises are also fairly universal, since humans mostly make the same kinds of noises. A sneeze may vary slightly in how it is written out, but it's near-universal in its interpretation (if you're a human). Same for a scream.