Most Hellenic army armoured vehicles carry a tactical plate holder on both sides. This is a square 40 cm x 40 cm frame which holds four metal plates that can display three shapes in orange or magenta. These are used during exercises to designate "friendly" and "enemy" forces and formations or units.
The use of this device begun around 1994 and it can be seen on almost all AFV types in Hellenic Army service, apart from the Leopard 2HEL, such as the M113 family vehicles, BMP-1, VBL armoured car, Μ109 family self propelled guns and their FDC vehicles. It has also been seen on a few soft-skin vehicles such as Hummers and Mercedes 240GD field cars.
You can download a .pdf file of the full-colour instruction sheet for this set of decals here