Some tires are directional which means that they have a correct direction of rotation, and some tires are asymmetrical which means they have different tread from inside to outside. (Goodyear and Goodrich have had tires in the past which were asymmetrical AND directional, that was nuts, and meant that you had specific tires for left and right!)

Directional tires have tread roughly shaped like and arrow and have a correct direction of rotation. This is like a tractor tire that has huge tread blocks forming a V pattern, and the purpose for it is the same as the tractor tire. When properly mounted, the tread on these types of tires disperses water but when mounted incorrectly, it will collect it. Or, mounted properly, this design will reduce hydroplaning, but when mounted backwards, it will cause it. So you really want your directional tires going the right way. If you have directional tires on your vehicle, they are simply marked by an arrow, and most of the time the word rotation, or direction of rotation, etc.

Asymmetrical tires have an inside and outside to their tread. Tire manufactures will often do this to optimize the traction and wear capabilities of the tire. An example would be a performance tire with an almost solid outside shoulder for cornering, a solid center rib for acceleration and braking, and a more open tread on the rest of the tire for better water dispersion. These tires are usually simply marked, inside, outside, this side out, or like our example; mount this side out.