For some time, I wasn't sure whether the company name Herring-Hall-Marvin should be hyphenated. It was a slow day and I looked over the evidence available, mostly photographs.

For the most part it was Herring-Hall-Marvin. Even in patents where they are named, the last one of which was granted in 1960. Just a few examples:

Click image for larger version.  Name: 1890s-HHM-note.jpg  Views: 9  Size: 61.4 KB  ID: 21920 Click image for larger version.  Name: Festus MO door1-10.jpg  Views: 9  Size: 456.8 KB  ID: 21921 Click image for larger version.  Name: HHM five star constellation two 2.jpg  Views: 5  Size: 70.3 KB  ID: 21922

But then it switches to Herring Hall Marvin and at the same time New York comes into the picture:

Click image for larger version.  Name: no Hiroshima Nippon Ginko 4 1958 patent.jpg  Views: 9  Size: 312.0 KB  ID: 21923 Click image for larger version.  Name: no Canyon Chop House Fort Collins 10 1966 small.jpg  Views: 9  Size: 113.4 KB  ID: 21924 Click image for larger version.  Name: no Savannah GA IMG_1170 small.jpg  Views: 10  Size: 187.4 KB  ID: 21925

The first non-hyphenated image is from Hiroshima and includes a 1958 patent date. The next is from a 1966 building. The third one I don't have a good date for but might be in the same time.

My best guess stems from the acquisition of HHM by Diebold in late 1959. Diebold may have added "New York" to the plate. And by removing the hyphens they might have distinguished their doors from the originals, and might have also bypassed trademark issues. As I said, this is a best guess.

Another possibility is that HHM went through bankruptcy, dropping the hyphens for the re-organized result, which Diebold later bought.

If anyone can fill in more details, please do so!