I probably have normal old man coarse whiskers. I haven't done any testing. I could go around, asking to feel old men's faces, I suppose.... Somehow, I don't think this would be well received. <eg>
We can laugh, but it's true!
I think sometimes it's obvious that someone's hair is unusually coarse / fine. For example, I had a friend (sadly passed) who kept a long beard, but his pure white hair was surprisingly soft and supple and you could tell just by the appearance. Conversely, sometimes you see guys of Mediterranean extraction whose hair looks particularly wiry.
But aside from these extreme cases it is very hard to tell.
Approaching a stranger with, "Excuse me, can I stroke your beard?" is likely to get you either punched or propositioned, depending on who you ask!