The answer is: Buttocks

Isaiah 20:2-4 - Isaiah walked naked and barefoot for three years as a sign against Egypt and Cush, symbolizing their impending shame and captivity.

In Isaiah 20, we encounter a rather startling and dramatic performance art piece by the prophet Isaiah himself! The act of walking around naked and barefoot for three years may seem extreme, but it was a significant means of communication in the Ancient Near East. Imagine the newspapers of the day: rather than providing headlines, Isaiah became a headline himself—a living testament.

The buttocks, mentioned as part of his sign, often symbolized shame and humiliation in biblical terms. The audacity of what Isaiah did was meant to shake the complacency of the Israelites and highlight the gravity of the circumstances regarding Egypt and Cush. People would be asking questions and giggling, but amid the silliness was a severe warning: The glory of these nations would surely fall.

This episode adds an interesting layer to the biblical narrative about the use of signs. Other prophets, like Ezekiel, also employed vivid symbols, often at great personal expense, to relay their messages. They had to capture attention in a time when visual action spoke louder than words—much like how videos grab us in today's busy world.

Among the prophets, Isaiah is often esteemed for his majestic poetry and rich imagery. He weaves narratives not merely to tell the future but to transform the hearts of the people. In essence, Isaiah's nudity doesn’t just shock—it reflects the naked truth of human folly and divine warning. So, when you think of fancy prophecies, remember Isaiah not only conveyed heavy truths but also embodied them in the most transparent way!