1. A system for signature detection, comprising: a memory; and a processor, coupled to the memory, to: acquire an article defect density map comprising a plurality of sections corresponding to a first resolution level which is indicative of defect numbers for the sections, and to determine a distribution representative of the defect numbers or function thereof; determine a threshold in accordance with said distribution, and to identify sections, out of said plurality of sections in the article defect density map, with defect numbers or function thereof above the threshold; and cluster at least part of adjoining identified sections, into one or more signatures, and thus configured to detect said one or more signatures.