I bought this many years ago from a dealer who had several helmets that appeared to have come from a local American Legion post. I picked up this helmet along with a "hate" belt. He had several painted US M1917 helmets. This cost me about USD$35 about 15 years ago, so I don't think the dealer was trying to cheat me with a fake paint job and artifical weathering.
I call it a flowerpot because of the rust markings on the inside and the extra holes in the side. It appears to me that this was mounted in some sort of a stand upside down. Notice what appears to be the shadow of square nuts or bolt heads . The rust markings on the interior look like the helmet was constantly damp, but kept level. If anyone has better thoughts the extra holes, please feel free to voice them!