the amount of times a person talks about drugs (IRL) is usually indirectly proportional to actual drug use...
I like this response. Often I find people who enjoy psychedelics to be much more vigorous and locked on in conversations, rather than lazily listening and occasionally offering slight counter points.You can normally tell when they have a specific twinkle in their eye, while either sober or not.
Pretty easy... just nonchalantly say "I wonder what music looks like?" The ones that smirk are psychonauts...
Music taste. Art taste. General tastes.