eng - cannot help with EGSS, but I assume it is the same as EGKK? Stands are marked eg 52L/52/52R (NB 'fictional' stands), and the yellow lines (there would be three in this case) line up with each of those. If allocated '52L', it would be the left line etc etc.
Best ring EGSS BAA Ops (D Officer?)- they mark out the stands.