Received by Alan G3NYK in Ipswich, England on 137.777 kHz at about 0330Z 18 May 2003 (coincidentally Marconi's patent for tuned detection was numbered 7777).
It's a plot of Hz offset vs time with the pixels indicating relative signal strength. 300 Hz is 137.780 kHz. (Argo software thanks to I2PHD) The elapsed time is about 1.5 hours. FFT integration time was about ten seconds and the transmitter took 72 seconds to send a dot, the first two of which require a bit of effort to see. It says:
dot-dot-dot-dash dash-dash-dash dot-dash-dash-dash-dash dash-dot dot-dash
Thanks to Alan Melia G3NYK in Ipswich. He provided a lot of advice and received the actual signals. The transmitter was 125 watts Class E and the aerial was 150 metres long (less than 7% of a wavelength). Aerial current was 1.65 amps and its efficiency was less than 0.1%.