The type of printing I'm thinking of was done at the time the print was made, but the lettering/printing was black. So, it may have just been some type of stencil that the photographer had made up. I thought I had read about some other device that could "burn" the photographer's name onto the paper, but I may have been mistaken.
since the lettering is black, it means there is no emulsion
maybe the photographer did something totally crazy-low-tech like
use a rubber stamp and ink ....
silver magnets, trickle tanks sold
artwork often times sold for charity
PM me for details