Hi Bogdanm, thanks very much for the quick reply.
Most of the time is that it will just appear in the LED display of Duo2 when I switch it on. After I see this, I will go to “Information”, but could never see any info to do with this symbol. This flickering symbol I had drawn above is not very accurate, the middle of the brackets is a big dark dot, something like that.
Hi Aliraza63, thanks for your reply.
Hi Nunigaia, yes, it is. So that LED display is call VFD display, sorry for my weak knowledge in Enigma. Thanks very much for the answer.