Note: The following information is courtesy of led-zeppelin.org
The Martin D-28 Dreadnought Acoustic debuted at the Bath Festival of Blues & Progressive Music Festival on June 28, 1970, when Jimmy Page played The Boy Next Door (That's The Way). Page continued to use the Martin for That's The Way and Bron-Y-Aur until the end of the 1970 US Tour on September 19, 1970.
The Martin was next seen on the 1973 European Tour, when Page played it for Bron-Y-Aur Stomp. For the 1975 Earls Court shows, Page played the Martin D-28 Dreadnought Acoustic for the acoustic set. To increase the quality of the sound, Jimmy Page used a Barcus-Berry Model 1355 Transducer, connected to a Barcus-Berry Model 1330S Preamp.
Page acquired a second Martin D-28 for the 1977 US Tour, presumably for the different tunings of the various acoustic songs. The primary Martin D-28 was marked with a small white star in the center of the pickguard.
TODO: See if Jimmy used the Martins for studio work.