وَلَوْ نَشَآءُ لَأَرَيْنَـٰكَهُمْ فَلَعَرَفْتَهُم بِسِيمَـٰهُمْ ۚ وَلَتَعْرِفَنَّهُمْ فِى لَحْنِ ٱلْقَوْلِ ۚ وَٱللَّهُ يَعْلَمُ أَعْمَـٰلَكُمْ Qur’an Muhammad (47:30)Walaw nash a o laarayn a kahum falaAAaraftahum biseem a hum walataAArifannahum fee la h ni alqawli wa A ll a hu yaAAlamu aAAm a lakum
Lit., "by their marks": implying, elliptically, that God does not grant to anyone a clear insight, as by a visible mark, into another human being's heart or mind.
Lit., "the tone (lahn) of speech": indicating that a true believer recognizes hypocrisy even without a "visible mark" (sima).
Evil is not always necessarily branded in this life with a distinguishing mark or brand. But the discerning ones know. Evil is betrayed by its speech and behaviour.