That's either an M35 or M40 helmet, distinct from the later M42 because of the rolled edge on the helmet skirt. The decals - if they are authentic - mark it as a police helmet. The Q64 stamping identifies the manufacturer - Quist - and the size of the shell, 64 centimeters. Because it's located on the side rather than the back of the shell, this particular helmet was probably made prior to 1943, but how much so I can't say. Without handling it in person, I can't say whether it's authentic or a good reproduction.

Pictures would be useful to identify them. Do you have any you can edit to your comment?