According to Elmhurst College, NH3, commonly called ammonia, is polar. Ammonia molecules have a trigonal structure that concentrates its three hydrogen atoms at one end, leaving a partial positive charge at the other end where the nitrogen atom has only one electron present.
Ammonia's polarity can be observed without determining its Lewis structure. According to Wikipedia, ammonia is miscible with water. Water is a polar solvent, and it forms covalent bonds only with polar solutes. Ammonia's ability to dissolve in water and remain in solution until energy is applied to break its covalent bonds with water marks it as a polar compound.