Menorca is the most lovely quiet and friendly place, it can be easy to let your guard down when on holiday on such a wonderful island.
However, leave NOTHING of value in your hire car whether on show or not.
We visited the wonderful Favaritx lighthouse last week, unfortunately it seems whilst we were there some lovely person forced entry to the passenger door and was then able to access the boot where one of our group had left a purse containing a sum of money, which was taken. The damage was only slight so we didn't notice immediately, and then only because the dent stopped the window from closing fully.
Also make sure you are fully insured on your hire car, as even if you don't cause the damage you could be expected to pay for it.
Please don't let this put you off visiting Menorca, it is a wonderful and generally crime free place.