Copyright "ear tags" are found on the opposite side.
Many of these masks were used as a give-away items or contest prizes in advertising campaigns, such as the Snow White Jingle Club. The Pennsylvania-based Stroehmann's Prize Winner Bread was one of the local bakery sponsors as noted by the imprint on the back of the mask. They even sold Snow White cake too!
Pictured with the Grumpy mask is the original mailing envelope in which it was delivered. The postage at the time from NY to IL cost only 1¢.
The return address is from Mickey Mouse Magazine, C/O Kay Kamen in New York City. The mailing label is marked "masks" and was sent to an individual (not a business sponsor). "Billy" was probably a participant in some sort of contest.
It's interesting to note that only four of the five masks are shown in the 1938 Kay Kamen-prepared guide book, Advertising and Merchandising Campaign for Bakers. Grumpy is not pictured.
Book page via Hakes.
One of the book's suggestions was to use the masks as give-aways at Halloween.