This is part of the artwork on the wall where the M2 line leaves the Yenikapı Metro station. The M1, M2, and the Marmaray all converge at this station. The Marmaray is the new train that goes under the Bosphorus, linking the European side of Istanbul with the Asian side.
Leave the lizard at home
In case you were wondering, there are no reptiles allowed on the Istanbul Metro system. Apparently, an arachnid or two would be just fine.