File:US 421.svgDescriptionUS 421.svg English: 750 mm × 600 mm (30 in × 24 in) U.S. Highway shield, made to the specifications of the 2004 edition of Standard Highway
File:US 421 (1948).svgDescriptionUS 421 (1948).svg 1948 style US Route 421 highway marker Date 7 January 2011, 16:51 (UTC) Source File:US XX (1948).svg Author Fredddie, Levente
File:US 421 (1961).svgDescriptionUS 421 (1961).svg 1961 style US Route 421 highway marker Date 13 December 2010, 07:30 (UTC) Source File:US XX 1961.svg Author Fredddie, Scott
File:US 421 (1926).svgDescriptionUS 421 (1926).svg Generic U.S. Highway marker, labeled for city use, from the First Edition of the Manual and Specifications for the Manufacture