LED LD3 is blinking a pattern of the SOS singal (...---...) with 1.5 sec pause between repeated loop steps.
Nothing special.
Just instead of "linear" pattern, LD3 is blinking something with a meaning. SOS Morse code is selected.
P.S. Possible upgrade: reaction to jumper setting on D2(PA12) to GND to change a pattern. Is with version is not done.