The most universal mammal behavior I know of is not visual, it's the "hi I'm here" bark or grunt. It's something that was pointed out in a wildlife tour video where they visited mountain gorillas: if you don't make any noise and their first indication is visual, you may have predatory intentions, but if you add a little "mm" noise, you're just passing through and they can relax.

It works for many kinds of creatures, humans included.