Each manufacturer usually has its own “code” for determining the fillings of the chocolates in their chocolate hearts. If you find a manufacturer whose chocolates you enjoy, get to know their codes. A swirl with two loops on it may mean caramel for one company and buttercream for another, but it will generally always mean the same thing for a brand.
Beyond codes, look for signs of nuts (large bumpy surfaces) or coconut (small bumpy surfaces). Hard caramels are typically square or rectangular, and soft caramels are typically flat and round. Chocolates that are wrapped sometimes have liquid or softer centers (like cherry cordials, for example).
Some manufacturers provide “maps” for their treats or photos that identify the fillings inside the box to help you identify what you’re about to enjoy. But, of course, the best way to find out what’s inside of your chocolate is to taste it!