The Historical Marker Database – “A catalog of public history cast in metal, carved on stone, or embedded in resin. This website is an illustrated searchable online catalog of historical information viewed through the filter of roadside and other permanent outdoor markers, monuments, and plaques. It contains photographs, inscription transcriptions, marker locations, maps, additional information and commentary, and links to more information. Anyone can add new markers to the database and update existing marker pages with new photographs, links, information and commentary.” [h/t Data is Plural]