The piece of colonial propaganda you are referring to is likely the famous "Join, or Die" political cartoon attributed to Benjamin Franklin. In this cartoon, the image of a segmented snake symbolizes the American colonies. Each part of the snake indeed represents a different American colony.
The idea behind the cartoon was to convey the message that the colonies needed to unite in order to be strong and to effectively resist British oppression. If the colonies remained divided (like the segments of the snake), they would be weaker and more vulnerable to external threats. Therefore, each segment of the snake symbolizes a different American colony, illustrating the need for cooperation and unity among them.
In summary, within the context of this propaganda, each part of the snake represents a different American colony, highlighting the necessity for unity in the fight against British rule.