MARKING : 133
You can see the 133 marking in the back view on the middle, left,
just before the bend at the bottom starts.
and as National's marking style -- the numbers are in script.
National sold their doorstop unpainted for 50 cents or
electroplated with brass, copper, or nickel for $1.80
per National's 1920's Catalog.
They also sold paint kits or their doorstops painted.
There is a very similar cast iron piece that is a Room Humidifer
that sits on an old finned radiator. You may see this item under
"COMMON MISCONCEPTIONS" on the Home page.