A. Yusuf Ali:Translation:
Had We so wiled, We could have shown them up to
you, and you shouldst have known them 4854 by
their marks: but surely you wilt know them by the
tone of their speech! And Allah knows all that you do.

Muhammad Asad:Translation:
Now had We so willed, We could have shown them clearly to thee, so that thou wouldst know them for sure as by a visible mark: 35 but [even so,] thou wilt most certainly recognize them by the tone of their voice. 36 And God knows all that you do, [O men;]
4854 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.