This is heading to Salisbury (and on to Cardiff judging by the WR maroon, including RMB coach 4th from loco) from Portsmouth & Southsea.

If going to Portsmouth & Southsea the headcode would be positions 2 & 3, ie. both discs on the smokebox door. The headcode shown, if in the Portsmouth direction, would indicate to Portsmouth Harbour.
Portsmouth & Southsea was unusual in that trains from all originating points carried the same positions 2 & 3 headcode. From Portsmouth and Southsea the usual individual route headcodes were displayed which were the same as to and from Portsmouth Harbour.