Hi - this is my first post!
I found a stamp in an old collection and it appears to be Sweden SG 50 (from my 1969 SG Europe catalogue). It is of average quality with a thin and an ugly postmark. However, the Crown watermark is inverted and this is not in the catalogue. Perhaps though it is in another more specialised catalogue.
Have I got something of interest here - and how much would something like this be worth?