Prohibited Matter

This aerogramme form was sent from Kingston, Jamaica (slogan cancel 9 JAN 1956) to Detroit, U.S. On the writing panel there is a hectography of a sweepstakes winnings list. 

The U.S. Postal Laws and Regulations banned specific contents, e.g. lottery tickets, from postal items. This is the reason for the 2-line handstamp "Supposed to contain matter / Prohibited importation".