I found this photograph of an Atchinson, Topeka & Santa Fe Class C 3 steel caboose on the internet.

This particular caboose, was photographed at El Paso Texas in the year of 1968. The Atchinson, Topeka & Santa Fe embarked on a major steel caboose rebuilding program between 1966 and 1968. Originally painted in a very plain primer like Mineral Brown or Box Car Red color schem with very minimal markings in the form of reporting marks initials that read A,T,S,F...these caboose were rebuilt with fewer windows, a bright red color scheme with a big yellow Santa Fe logo below the cupola and cushioned underframes.

The Santa Fe Class C 3 caboose that is shown here, were modified from the older standard steel cupola cabooses from the steam era, but did not recieve the refinements that the Class C 1, C 2 and C 4 Class cabooses recieved during the rebuilding.

The C 3 car shown here with the yellow painted cupola, retains it's original steam era sliding side windows.
The C 3 Class cabooses, were not used on road freights, and were restricted to slow moving transfer freight trains. These cars did not recieve the cushion underframes during their rebuilding.

This is a basic and relatively un modified Santa Fe steam era caboose with a new paint job and little else.