Why is a plus sign used for hospitals?

It is not an internationally accepted sign for identifying easily for a stranger who does not know the language of the region. We have swallowed this cross symbol of Jesus Christ silently along with the 'English Medicines' . Even the Arabs know this. They have a crescent moon with a wine glass and a snake round it to represent drug store or a hospital. It is high time Hindus must have an OM mark for that.