JIM FOX Emails 26 Aug. 2018: We THINK the plate T-687 was used by the “Federal Works Agency”, with the “T” denoting a “truck”.
The Agency existed between 1939 and 1949, but Federal issues were standardized in 1942, so this one would appear to have been issued between 1939-1942, when the unified plates with the “shield-shaped” border came into use.
Europlate blog 
JIM FOX Emails 26 Aug. 2018: We THINK the plate T-687 was used by the “Federal Works Agency”, with the “T” denoting a “truck”.
The Agency existed between 1939 and 1949, but Federal issues were standardized in 1942, so this one would appear to have been issued between 1939-1942, when the unified plates with the “shield-shaped” border came into use.
Thanks Jim.