[tomjen3]

Box if you are overwriting the next char, vertical bar if you are inserting. Dunno whenever you would use underline (I guess if it doesn't work with box for some reason)?

Thats the standard, anyway, so if you don't follow that, you are confusing your users.

[samatman]

The standard in modal-land is box in normal mode and bar in insert mode. R for overwrite is an underline.