It is a common feature of multi player PCBs to have a small window where one can look in and see a number for each layer of the PCB. It's used in manufacturing to show that all layers are included I believe.
We use Altium, which is easy enough to put this window in a signal layer, as it just needs to be added. However, when we come to plane layer it seems to get complicated. We can put a window into the plane without issue, but we cannot find any way to get numbers written on it.
Talking to our Altium support, they don't seem to have any ideas either. Has anyone done this? Does anyone know how to add the required text to this window?