IBM 3270 Manual page 33

Using Alternate Case - the Marks on the
Front
You will notice that some of the keys are labeled
on the front. For example:
Jump
R
~
Alternate
ease
ChgSc
The markings on the front are for the alternate
function.
For alternate case, press and hold the Alt key
and then press the key you want.
3-4 Book 3 - Using the Control Program