And when they see an Ayah (a sign, a proof, or an - Surah As-saffat ayat 14 in English

﴿وَإِذَا رَأَوۡاْ ءَايَةٗ يَسۡتَسۡخِرُونَ ﴾
[الصَّافَات: 14]

And when they see an Ayah (a sign, a proof, or an evidence) from Allah, they mock at it

﴿وإذا رأوا آية يستسخرون﴾ [الصَّافَات: 14]

Al Bilal Muhammad Et Al
And when they see a sign, they turn it into mockery

Ali Bakhtiari Nejad
And when they see a sign they ridicule

Ali Quli Qarai
and when they see a sign they make it an object of ridicule

Ali Unal
When they see an extraordinary evidence (of the truth, a miracle), they take it in mockery (and call others to do the same)

Hamid S Aziz
And when they see a sign they incite one another to scoff

John Medows Rodwell
And when they see a sign, they fall to mocking

Literal
And if they saw/understood an evidence/sign/verse, they humiliate/mock/ridicule/undermine

Mir Anees Original
And when they see a sign they seek to mock

Mir Aneesuddin
And when they see a sign they seek to mock