fringe-cursor-alist

fringe-cursor-alist is a variable defined in `C source code'.
Its value is

((box . filled-rectangle)
 (hollow . hollow-rectangle)
 (bar . vertical-bar)
 (hbar . horizontal-bar)
 (hollow-small . hollow-square))

• Automatically becomes buffer-local when set.

Documentation:
Mapping from logical to physical fringe cursor bitmaps.
The value is an alist where each element (CURSOR . BITMAP)
specifies the fringe bitmaps used to display a specific logical
cursor type in the fringe.

CURSOR specifies the logical cursor type which is one of the following
symbols: `box' , `hollow', `bar', `hbar', or `hollow-small'. The last
one is used to show a hollow cursor on narrow lines display lines
where the normal hollow cursor will not fit.

BITMAP is the corresponding fringe bitmap shown for the logical
cursor type.