I suggest you NOT to hand it over to the security.  I once found a watch on the beach. I  handed it over to the security and posted a notice here. The owner contacted me through this site and I directed him to the relevant security office. Subsequently the owner told me that the security office did not have the watch when he contacted them (despite the fact that the office took down my personal particulars when I handed in the watch).  I suggest you hand it over to the police instead.