يُعْرَفُ الْمُجْرِمُونَ بِسِيمَاهُمْ فَيُؤْخَذُ بِالنَّوَاصِي وَالْأَقْدَامِ (The guilty ones will be recognized [ by the angels ] by their marks and will be seized by foreheads and feet...55:41). The word sima means 'a sign'. Hasan Basri (رح) says that the day when sentence will be passed against the guilty to go to Hell, the following will be their signs: They will be known by their dark faces and their blue eyes. Through grief their faces will turn pale. The angels will recognize the guilty by these signs and seize them.
The word نَّوَاصِي nawasi is the plural of نَاصِیۃُ nasiyah, and means 'forelock'. Some will be dragged by their forelocks, and others will be dragged by their feet. Or it could mean that sometimes they will be dragged by their forelocks and at other times they will be dragged by their feet. The third explanation could be that the angels of punishment will bend their foreheads down to their feet and tie the forelocks to the feet, and throw them into the Hellfire. Allah knows best!