Allah said;

[فَأَخَذَتْهُمُ الصَّيْحَةُ]

(So the Sayhah overtook them) This is the piercing sound that came to them when the sun rose, which was accompanied by the city being flipped upside down, and stones of baked clay (As-Sijjil) raining down upon them. The discussion of As-Sijjil in Surah Hud is a sufficient explanation. Allah said:

[إِنَّ فِى ذَلِكَ لآيَـتٍ لِلْمُتَوَسِّمِينَ ]

(Surely, in this are signs for those who see.) meaning that the traces of the destruction of that city are easily visible to any one who ponder about it, whether they look at it with physical eyesight or mental and spiritual insight, as Mujahid said concerning the phrase,

[لِلْمُتَوَسِّمِينَ]

(those who see) he said, "those who have insight and discernment.'' It was reported from Ibn `Abbas and Ad-Dahhak that it referred to those who look. Qatadah said: "those who learn lessons''.

[لِلْمُتَوَسِّمِينَ]

(those who see) therefore the meaning is "those who ponder''.