Good morning, MagKelly;

The "Toko" designation I believe to be a contraction of "Tokyo Kogaku K. K." That was the name of the company around the time of World War II. Later in the 1950s they shifted slightly to "Topko," sort of a concession to the English speaking photographers they were encountering, and was for "Tokyo Optical Company," sort of. Later they became the much better recognized Topcon brand name here in the United States. They were one of the earlier companies to adopt the SLR camera design, and I believe that they were the first in Japan to use a Through The Lens (TTL) light metering design.

As a minor point of interest, the US Navy thought enough of the Topcon SLR camera (possibly the Topcon Super D) to have bought a large volume of them in the 1960s for their photographers to use in the performance of their official duties. The Nippon Kogaku K. K. Nikon F was not the only Japanese camera the US Navy used.