The digital display is always reference true north. The Arrow wind reference depends on what screen you have selected.
For ARC mode
Speed and Wind Indications
In any of the ND modes, the following data are displayed on the L upper corner of the ND:
...
- wind origin and force digital values in degress and knots, the wind origin is given with respect to the true North)
- wind direction in analog form, represented by means of a green arrow orientated with respect to the true north. This arrow is
displayed only if the wind force is greater than 2 knots..
For ROSE modes
In the left upper corner, the A/C actual ground speed and true
airspeed indications are provided, as well as the wind data
(direction/force: the direction is given with respect to the
true North in digital form, and with respect to the heading
dial axis (aircraft heading) in analog form (arrow).
Info all in the A320 AMM