Cadillac 1995 DeVille Owners Literature page 75

The square key is for
the ignition only. It has
a resistor pellet which
is part of the vehicle's
PASS-Key
I
13' system.
The oval is for the
doors and all other
locks.
When your new Cadiilac is delivered, the dealer removes the plug from
the door key. The plug
has a
code on
it
that tells thc dealer or a qualified
locksmith how to make extra keys. However, the ignition key does not
have the knockout plug. The ignition key has a bar code tag attached to
it.
Your dealer or qualified locksmith,
by
reading the bar code tag, can then
make your ignition key.