A real case study and characterisation of modern energy efficient windows allowing mobile communication is presented. An earlier study had shown that laser scribing of energy saving coatings allows highly reducing the microwave attenuation (from 30 to 1-3dB) using a wide band-pass frequency-selective surface (FSS) while preserving the thermal quality of the window. To achieve large-scale production, the laser scribing technique has been further developed. The effect of laser scribing on the mechanical properties of a substrate has been determined through mechanical strength tests. Moreover, the insulating properties of the window have been analysed to ensure the reliability of this technology. As a real case demonstration, an entire train has been equipped with prototype windows. The signal quality has been controlled for a wide band of frequencies and for existing technologies such as long term evolution, universal mobile telecommunication system, multiple input multiple output and for different configurations such as a stationary and a moving train.