That's like being relieved your classic vintage bike is made of gas pipe, not Reynolds or Columbus tubing.

Seriously, it's easy to tell the difference. If you look at the pictures Scooper posted, you'll see the edge of the base tape on the tubular. Often it's peeling back and has loose hanging threads when it gets older. The sidewalls also look messy after a while with smears of glue. You won't see a brand new bike with tubulars in a bike shop these days, but the tires would look flat all the way around when there's no air in them, which would be about a week after they've been inflated. Nevertheless, tubulars must still hold a slight performance edge over the lightest and fastest clinchers, because many racers still use them.