From a previous SC thread on war tax overprints about the Thompson overprints if you card is indeed one.
"British Colonials had been extensively issued up to that time
with "War Tax," and War Stamp" overprints, and the United
States had just recently entered the fight. Increased taxes,
in consequence were a foregone conclusion and with
discussion of an increase in postage rates, there was some
philatelic agitation for a special U. S. "War Tax" stamp issue.
Within a short time some of the 1¢ green stamps of the then
current issue were seen in philatelic mail from the Pacific
Coast, the stamps bearing a bright red overprint, "WAR
STAMP."
They had been produced by Charles S. Thompson, well
known philatelic writer, of Los Angeles, and he was using
them on all his mail, two cents for postage and one of the
overprinted 1¢ stamps as an additional rider. I believe he
thus hoped to influence Uncle Sam toward a specially
designated issue, but the Post Office Department failed
to adopt the suggestion.
When the ultimate increase in postage was passed by
Congress in October of that year, as Mr. McGee relates
in his article, no special issue was forthcoming and the
ordinary regular stamp issued were made to suffice.
The U. S. "WAR STAMP" overprints are still seen
occasionally in collections that were in formation during
that period and are regarded as interesting philatelic
mementos of World War I days.
- George B. Sloane
Sloane's Column
Stamps
March 18, 1944"
Here is a link to that thread
https://goscf.com/t/16417