We report here the feasibility study of anti-counterfeiting low-cost nanostructured flexible security tags for the tracking of large-scale fabrication products, such as pharmaceuticals or original equipment manufacturers. The fabrication process makes use of the mature nanotechnology called Template Synthesis to shape thin track-etched polymer film into covert laser readable tags, combining random self-organized structures with organized patterns. Techniques are developed to drastically limit the number of fabrication steps and keep fabrication costs low, while opening to numerous adjustment parameters. A dedicated, simple optical setup is presented, to capture speckle images of such tags lightened up by light emitting diodes or laser beams. Speckle images are analyzed in terms of encoding parameters, found here quite numerous to ensure a large coding range of large-scale production batches. We particularly highlight ultra-dark areas in speckle images, where nanowire structures completely inhibit speckle patterns. This unique, high-contrast optical feature addresses these low-cost nanostructured thin films to provide a very promising solution for large-scale security tags.