2003 Ford Taurus Theft light flashing?

My 2003 Ford Taurus ran fine this morning. My mom just came home and told me my Theft light is flashing every few seconds. The car started just fine but the light didn't stop flashing like I thought it would. I don't have the manual for the car anymore. How do I make it stop?

You can find the manual online (for free online viewing) new enough that Ford probably has it on their site.

But first try setting the alarm and then turning it off - that should reset the system - or you can disconnect the battery for a few seconds (though that also removes your radio presets)