Anomalous enhancement of Raman scattering has been detected for tungsten oxide thin films deposited on indium tin oxide (ITO) coated glasses subjected to proper annealing treatment. Raman scattering enhancement is triggered by the presence of sodium oxide on the samples surface due to a thermal induced diffusion of sodium ions from the glass substrates to the upper layers as revealed by Photoelectron Spectroscopic investigations. A deeper analysis of the sample local morphology and elemental distribution is performed by Scanning Electron Microscopy with an Energy Dispersive X-ray detector.