Thank you gentlemen.
I have the original 1961 stamp, and had a suspicion that this SS could be something other than regular issue stamp, but wanted to make sure that I'm not simply going blind.
I guess I'll catalog this as something like poster stamp.
I'll give it my own Scott number. It will fit nicely right after 3844 which is also commemorating same event. So it is officially Scott #3844A in my books
Low value does not surprise me, as there seems to be several hundred thousands of those issued judging by the number 272,928.