Actually, it depends on what game you're referring to. If talking about the 3rd generation, then Attack and Special Attack are defined by their types, and there SHOULD be something about which ones are which on the main site.
If you're referring to D/P, then there will always be symbol beside it, telling you what kind of attack it is. If it's a red-orange symbol, and has what looks like a 'blast', or 'explosion' of some sort on it, it's a physical attack. If it's a dark blue, and has a horizontal oval on it, then you have a special attack. Or, in the case that it's neither, it would be gray with some .. type of symbol on it, I forget though.