IBM 5155 Manual To Operations page 204

The characters on the front faces of the keys are special
ones you may need when programming in computer
languages, such as BASIC. These characters are not
present on the US. English or U.K. English keyboards,
but you should keep them in mind if you ever want to
use a language other than English. If you are using a
~
National DOS diskette for either UK. English or US.
English keyboards, you may want to set up a National
DOS diskette now for another language so that you can
try this example.
To type one of these characters, hold down the Alt and
Ctrl keys (these keys are below and above the left Shift
key) and press the key with the desired character on its
front face.
Example:
Press and hold
[J8J
and
[ED
Press the key with the [ character on its front face.
The left hand bracket (D appears on the screen.
The four-keystroke Alternate characters are available
to you with every keyboard. The characters are the
same for all keyboards. They enter special three-digit
ASCII codes to display characters that you could not
otherwise type.
3-16 Keyboard