"And We have left it as a sign" for those who come after them, meaning: the ship.

Muhammad (Ibn Abi Zamaneen) said: His saying "as a sign (ayah)" means: a mark or token, so that they may take a lesson from it.

"Is there, then, any who will receive admonition?" meaning: any who will reflect? He commands them to take a lesson and to beware that there might befall them what befell those (before them).

Muhammad said: "Mud-dakkir" is originally "mud-takar" (an active participle from the root dh-k-r). The 'dhal' was assimilated into the 'ta', and then it was transformed into a doubled 'dal'.