What does the "T" shape mean here?
There is a logogram, but I want to know the RTA's left side port whether is config the
192.168.1.0/24 network segment's IP address.
This is Quidway technology.
It represents a multi-access local network, such as ethernet. It's just drawn vertically so looks a little unusual.
It shows that the network address on the left is
192.168.1.0/24, but doesn't specify the address of the interface of RTA. The network on the right of RTB is
192.168.2.0/24, again without specifying the address of the interface of RTB.
It's not a letter T, it's the connecting lines to other devices on that network segment. However since there are not any other devices, that is simply the artists choice as how to represent such a segment. If there were additional devices, then you would see the lines extended to accommodate the additional devices.
Also, just because it's a plain, flat line doesn't imply anything about the underlying technology (e.g. ethernet), it's just a generic link.