Trans-polyacetylene is evidenced by surface enhanced Raman scattering (SERS) in diamond films prepared by hot filament assisted chemical vapor deposition from C${\mathrm{H}}_{4}$ and ${\mathrm{H}}_{2}$. The analysis of the Raman spectra for different excitation energies shows that the deposited trans-polyacetylene is composed of chains exhibiting short conjugation lengths. Together with polyacetylene, diamond crystals of nanometric dimension are evidenced by both SERS and high resolution transmission electron microscopy.