SPI means Shunt Permitted Indicator.However,conventional Shunt signals like the one mounted on the main post are also called SPIs.However the function of the special signal is difficult to guess unless the yard layout is studied closely or maybe someone...

SPI means Shunt Permitted Indicator.However,conventional Shunt signals like the one mounted on the main post are also called SPIs.However the function of the special signal is difficult to guess unless the yard layout is studied closely or maybe someone could ask the station staff?It seems the signal is an improvised unit and has a mesh grille on both the sides which implies that its meant to be visible from both sides?One purpose of the SPI may be to indicate the route and is displayed in conjunction with the shunt signal.

This is a Shunting Permitted Indicator (SPI) and works in conjunction with a stop signal or a shunt signal. The SPI shows a yellow cross illuminated by light and authorises the Driver to shunt past the associated stop/shunt signal in the ‘On’ position. ...

This is a Shunting Permitted Indicator (SPI) and works in conjunction with a stop signal or a shunt signal. The SPI shows a yellow cross illuminated by light and authorises the Driver to shunt past the associated stop/shunt signal in the ‘On’ position. A proceed hand signal must always be shown at the signal.