black metal frame, white matte, marked 4/15.

The image is a stand-in, we don't have an image of this 4/15 impression.

I'm pretty sure this is a reference to 'The Chief', a famous locomotive on the Santa Fe railroad. That's the engine front and center, upper-right is the Portland Union Station clock tower, and those might be different kinds of rail cars peeking over the hill at their 'chief'.