The receiving station has not filtered out @. It seems that AIS
transmitters will send @ as fill character if the ship name
definition is not made properly.
Or otherwise it is some AIS transmitter brand property because not
all ship names, even short ones, do not have @-filler.
When I was setting up my AIS receive station with DireWolf program I noticed the same with some ships. I had to do @ filtering before sending them to arps.fi to get rid of names with @@@ strings.