I already had this 1969 stamp from South Africa, but these control blocks were for sale for just a few dollars, and I bought them.
The two control blocks were printed on different types of postage stamp paper.
(Are these two distinctly different postage stamps— and should the philatelist put one of each in his or her album? I say yes: if you have both types, put both in your album.)
When the stamps are held up against a light, it’s easy to see the watermark clearly, in the white margins of the block.
These are some of the last South African stamps issued with watermarks.
In the United States, stamps with watermarks were issued only for a short time— from 1895 to 1916.