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METAL TABS 1942-1955. Until 1941, new license plates were issued yearly, and every vehicle got a new pair of plates every year. Shortage of metal in World War II led to keeping the same the license plates and issuing only a year tab to renew. (1942 used a metal strip that covered the entire top of the plate, 1943 used a V for Victory tab, and 1944 used only a window decal.) Most years need two metal tabs, front and rear (1946, 1954 and 1955 being the exceptions, they use only one tab in the rear).

Source: http://reviews.ebay.com/DMV-Clear-C...951-1956-1963-YOM?ugid=10000000000961771