There is no button, I probably took it off as a kid. But I know it was given to me in about 1965 and it was new then, so there's no question about the date, give or take a year. I don't think the colors were ever as bright as on the example in Steiffgal's post. I think the white was always more of a cream color. It's not dirty, but it could have yellowed/faded with age.
The one I saw priced at $135 was in the same kind of condition, but this was in a retail antique store, so I think a lot of that price is retail mark-up and pre-economic crash pricing. Probably would be good for an insurance value. Steiffgals estimate is probably right-on if for Ebay or collectors I would think.