fringe-indicator-alist

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

• Automatically becomes buffer-local when set.

Documentation:
Mapping from logical to physical fringe indicator bitmaps.
The value is an alist where each element (INDICATOR . BITMAPS)
specifies the fringe bitmaps used to display a specific logical
fringe indicator.

INDICATOR specifies the logical indicator type which is one of the
following symbols: `truncation' , `continuation', `overlay-arrow',
`top', `bottom', `top-bottom', `up', `down', empty-line', or `unknown'.

BITMAPS is a list of symbols (LEFT RIGHT [LEFT1 RIGHT1]) which specifies
the actual bitmap shown in the left or right fringe for the logical
indicator. LEFT and RIGHT are the bitmaps shown in the left and/or
right fringe for the specific indicator. The LEFT1 or RIGHT1 bitmaps
are used only for the `bottom' and `top-bottom' indicators when the
last (only) line has no final newline. BITMAPS may also be a single
symbol which is used in both left and right fringes.

Value:

((truncation left-arrow right-arrow)
 (continuation left-curly-arrow right-curly-arrow)
 (overlay-arrow . right-triangle)
 (up . up-arrow)
 (down . down-arrow)
 (top top-left-angle top-right-angle)
 (bottom bottom-left-angle bottom-right-angle top-right-angle top-left-angle)
 (top-bottom left-bracket right-bracket top-right-angle top-left-angle)
 (empty-line . empty-line)
 (unknown . question-mark))