Past research shows that luxury products can function to boost self-esteem, express identity, and signal status. We propose that luxury products also have important signaling functions in relationships. Whereas men use conspicuous luxury products to attract mates, women use such products to deter female rivals. Drawing on both evolutionary and cultural perspectives, five experiments investigated how women's luxury products function as a signaling system directed at other women who pose threats to their romantic relationships. Findings showed that activating a motive to guard one's mate triggered women to seek and display lavish possessions. Additional studies revealed that women use pricey possessions to signal that their romantic partner is especially devoted to them. In turn, flaunting designer handbags and shoes was effective at deterring other women from poaching a relationship partner. This research identifies a novel function of conspicuous consumption, revealing that luxury products and brands play important roles in relationships.