Chevrolet S10 Pickup 2003 Owner's Manual page 76

When a new vehicle is delivered, the dealer provides
the owner with a pair of identical keys and a key
code number.
2-4
This vehicle has one
double-sided key for the
ignition and door locks. It
will fit with either side up.
The key code number tells your dealer or a qualified
locksmith how to make extra keys. Keep this number in
a safe place. If you lose your keys, you'll be able to
have new ones made easily using this number.
Your dealer should also have this number.
Notice: Your vehicle has a number of features that
can help prevent theft. You can have a lot of
trouble getting into your vehicle if you ever lock
your keys inside. You may even have to damage
your vehicle to get in. So be sure you have spare
keys.
If you ever do get locked out of your vehicle call the GM
Roadside Assistance Center. See Roadside Assistance
Program on page 7-6