A new paradigm for coherent microwave polarimetric remote sensing observation of man-made metallic targets at sea is here presented and demonstrated over real polarimetric SAR data. It is based on the different symmetry properties of the sea and of the man-made targets. The rationale relies on physical principles instead of standard image processing. Hence, a simple and very effective filter to observe man-made metallic targets at sea by full-resolution dual-polarized Synthetic Aperture Radar (SAR) data is developed. The technique is compared to a classic polarimetric approach, namely the Polarimetric Cross-Entropy (PCE) Constant False Alarm Rate (CFAR), and it is shown to best perform. Experiments, undertaken over a large data set of Single Look Complex (SLC) L-band ALOS-PALSAR and C-band RADARSAT-2 full-polarimetric SAR data, demonstrate the physical soundness of the theory and the effectiveness of the approach from an operational viewpoint.