Vintage 1974 Postcard Hygroscope Weather Indicator Boy on Rocking Horse Used 6x4 For Sale

Curteich Linen Postcard Elgin Watch Building 1939 New York World\'s Fair Unused
Offered for sale is a vintage postcard, cancelled in 1974, showing a boy on a rocking horse. It is a \"hygroscope weather indicator.\" The blue area in the top left corner is supposed to change color. The postcard was published by Shackman, New York. It was printed in Hong Kong.

Please enlarge pictures for abetter view of the condition. Measures about 6 by 4 inches (15 x 10 cm).