There were "Mile 0" signposts put up at other locations than Dawson Creek. This one was at Whitehorse, Yukon, in 1942 - it actually marks Whitehorse as Mile 0 of the Northern Sector of the highway project. The sign on the Dodge weapons carrier says: "First truck, Dawson Creek to Whitehorse. Headquarters, Northwest Service Command. 1030 miles, 71 hours" - it arrived in Whitehorse on September 27, 1942.
The "Signpost Forest" at Watson Lake developed fairly slowly after its start in 1942, but as of 2015 it has over 72,000 signs. This photo was taken in the 1960s by Bill Lythgoe.