No Step on Snek is derived from the flag designed by the United States Navy during the American Revolution in 1775. The snake was inspired by a political cartoon drawn by Benjamin Franklin during the Seven Years' War. The snake represented the American colonies by its division into thirteen parts.
No Step on Snek means "don't walk all over the thirteen colonies" aka the United States. The symbol and the flag have come to represent American patriotism. Don't step on this snake.