"And when they see a sign," meaning when a sign is recited to them, "they mock," which comes from mockery (al-sukhriyyah).
﴿وَإِذا رَأَوْا آيَة﴾ إِذا تليت عَلَيْهِم آيَة ﴿يَسْتَسْخِرُونَ﴾ من السخرية
