The Wireless Emergency Alerts system was intended mostly to be for major emergencies where everyone needs to be notified (e.g. there's a tornado coming your way seek cover). Sending an alert to everyone in the middle of the night to look out for a license plate number is a poor use of the system. The net result is that many people got annoyed and are now deactivating what could be a very important resource in the future. Information such as "look our for a Tan Lexus" is best directed at people in a position to make use of it... e.g., notifying those out on the road via electronic road signs and radio broadcasts. Waking a city of 8 million up to give them information that is totally useless will just annoy people.

This was sent via the Wireless Emergency Alert and not a text message. It's a special alert that sounds a loud continuous tone (similar to the tone on TV/radio when they test the "Emergency Broadcast System"). It was automatically "installed" on most modern smartphones (at least in the NYC area) earlier this year. The default setting is "on" although users can disable the alerts (which apparently many in NYC are now doing).