Apparently "the first audio radio broadcast of voice and music occurred on December 24, 1906, when Canadian-American inventor Reginald A Fessenden transmitted from Brant Rock, Massachusetts. This historic transmission, heard by shipboard radio operators along the Atlantic Coast, included Fessenden playing the violin solo of 'O Holy Night' and reading from the Bible, marking the beginning of amplitude modulation (AM) broadcasting".

I wonder if that's what aliens would hear as the first sign of humans?