seat belt warning light?

[9musTang9er]

my fathers 66 convertible has this "seat belt" light under the ignition, i've tried looking for other ones but cant seem to find any? is this rare or a custom touch from the previous owner?

 

[t_chelle16]

I'm pretty sure it's standard.

In fact:
http://www.mustangsunlimited.com/itemdy00.asp?T1=SD97+01

-Chelle