Alien language (Blue Moon)
The alien species that had tried contacting Earth to aid the development of humanity around the 1950s to the 1960s contacted them in the species' own language. The language had an "unearthly, five note chord", and "alternated at seemingly irregular intervals but always maintaining a pure minor harmony". The script, as visualised by the TARDIS' "very sophisticated translation computer" consisted of "elegant" pictograms, concentric circles and minimalist lines.
The Tenth Doctor, having used the TARDIS' computer to translate the script, dug out a message of the surface of the Moon to get the alien species' attention. He told them humanity had to find their own way. The species left, with no trace of them by the time Apollo 11 touched down on the Moon. (PROSE: Blue Moon)