There is a unique serial number in the flash info block of the MAX32660. It is stored in the first 24 bytes (0x40000-0x40017). To read the information block you first must unlock it. It is a good idea to lock it back when you're finished. You can use the following two functions in flc.h to lock and unlock this block:
FLC_UnlockInfoBlock();
FLC_LockInfoBlock();