The Danio has a '3 channel' bow thruster. There are 3 channels, instead of 2 channels which is commen on seagoing vessels. The Danio has, ofcours, a channel to port and starboard and an additional running to the forward.
Here you can see a animation about it, although they show a '4 channel' bowthruster but the principal is the same.
http://veth.net/vervolg.php?pagina_id=105
This system, together with the one Bottman shows, is standard on European inland vessels.
Hard to say Austins theory seems right as there appears to be one midship aswell
The sign mid ship is the Plimsoll mark.
http://en.wikipedia.org/wiki/Plimsoll_line#Load_line