SI
Set Visual SI [ 'nnn | "char" ]
(Default=None)
If you edit text containing ShiftIn characters, they will not appear on the screen. Even worse, if there is ShiftIn character but no ShiftOut character preceding it on a line, the ShiftIn character disappears from your file when you press Enter. This is done “on your behalf” by the terminal or terminal emulator. To get around these problems, you can define another character as a translation for the ShiftIn character. For example, Set Vis SI “|” defines “|” to represent ShiftIn.
When Visual needs to print a ShiftIn on the screen, it prints a “|” instead. When Visual sees any “|” on the screen, it converts it into a ShiftIn internally. To avoid turning every occurrence of the “alias” character in your file into a Shiftin, Visual prints a “?” for any line with a valid alias already in it and will not let you update that line in Visual mode (use Modify instead).