Regular-shaped metal nanocrystals and their ensembles can serve as ideal substrates for studying surface-enhanced Raman scattering (SERS). We synthesized well-defined silver nanowires for a systematic study of SERS signal with respect to polarization and structural ordering. The observed dependence on polarization direction confirms prior theoretical predictions that large electromagnetic (EM) fields are localized in the interstitials between adjacent nanowires. We show that these modes are largely dipolar in nature and rely on short-range EM coupling between nanowires.