Optical properties of thin vapor layers are strongly affected by the influence of the boundaries. We study the transmission and reflection properties of a short vapor cell. The system is modeled as a thin layer between two parallel surfaces, filled with two-state atoms. The symmetry properties of the optical coherence with respect to the detuning of the light frequency from resonance show up in specific symmetries of the spectra. In the case of reflection, this symmetry depends on whether a quarter wavelength fits an even or an odd number of times in the layer thickness. Also the magnetically induced optical rotation and circular dichroism is discussed, both in transmission and in reflection.