Option C, "You may have just won a $500 gift card!", potentially violates CAN-SPAM specifications on subject lines because it can be considered misleading or deceptive. CAN-SPAM regulations require that subject lines accurately reflect the content of the email. Misleading subject lines that imply the recipient has won a prize when this is not the case can lead to violations of these regulations, potentially resulting in penalties. It's crucial for marketing communications to be transparent and not mislead recipients about the nature of the email content.