Isaiah 3 is a prophecy against Judah and Jerusalem, specifically targeting the pride and vanity of the women of Jerusalem. Verse 21, mentioning "the signet rings, the nose rings," is part of a larger list detailing the extravagant jewelry and adornments these women wore.

Here's a breakdown of what these items signify within the context of the verse:

Signet Rings: These were not just decorative rings. Signet rings were used to create an official seal. They were often a symbol of authority, status, and wealth. In this context, the mention of signet rings suggests that the women flaunted their importance and social standing through their expensive accessories.

Nose Rings: Nose rings were a common form of jewelry in the ancient Near East, including in ancient Israel. They were often a sign of wealth and beauty. The mention of nose rings adds to the overall picture of excessive adornment and a focus on outward appearance.

Overall Meaning in the Verse:

The inclusion of signet rings and nose rings in the list serves to emphasize the:

Pride and Vanity: The women are excessively concerned with their appearance and flaunt their wealth through extravagant jewelry.
Materialism: Their focus is on material possessions and outward adornment rather than on spiritual matters or righteousness.
Judgment to Come: Isaiah is warning these women that their pride and indulgence will lead to their humiliation and suffering during the coming judgment. The list of finery is not just a description but a prelude to the stripping away of their possessions and status.

In essence, the verse highlights the misplaced priorities of the women of Jerusalem, who prioritized external appearance and material possessions over genuine piety and righteousness, thus incurring God's judgment.