Chiang Mai Taxi Meter

In Chiang Mai, the second largest city in Thailand, most of the automobile taxis operate between the airport and the city center. They generally charge a flat rate of 150 baht (about $5.00 US) for this jaunt, so I don't know why they call them taxi meters as they don't usually turn on the meters. At least they're safe according to this sign at the airport. But what they're saving us from isn't clear. Did something get lost in translation or are they saving us from having to walk into the city ourselves?