Optical properties of layered materials can be controlled manipulating the discrete number of atomically-thin two-dimensional crystal layers. Unique amongst the layered transition metal dichalcogenides, ReS2 has optical emission that is linearly polarized and proportional to layer number. By reducing the temperature to 10 K, we show that this emission is distinctly polarized between two well-resolved excitonic emission peaks. The 90º anisotropy is highly layer dependent for 1 - 3 layers, indicating its origin to be from interlayer exciton coupling. The distinct spectral separation and anisotropy that emerge only at low temperature provides insight into the formation, evolution, and symmetry of low-energy exciton states in layered two-dimensional semiconductors.