A postcard from sometime between 1905 and 1910 depicting a vacuum tube (valve in UK) enclosing a pair of lovebirds...
The message at the bottom of the card says "A wireless message CQD" . CQD was the code adopted by Marconi as a maritime distress signal in 1904, SOS was adopted internationally in 1906 but CQD was still being used on some British ships up until 1012.
The Titanic Broadcast CQD when she was sinking.