We begin an investigation into the semantic patterns underlying user choice in passwords. Understanding semantic patterns provides insight into how people choose passwords, which in turn can be used to inform usable password policies and password guidelines. As semantic patterns are difficult to recognize automatically, we turn to visualization to aid in their discovery. We focus on dates in passwords, designing an interactive visualization for their detailed analysis, and using it to explore the RockYou dataset of over 32 million passwords. Our visualization enabled us to analyze the dataset in many dimensions, including the relationship between dates and their co-occurring text. We use our observations from the visualization to guide further analysis, leading to our findings that nearly 5% of passwords in the RockYou dataset represent pure dates (either purely numerical or mixed alphanumeric representations) and the presence of many patterns within the dates that people choose (such as repetition, the first days of the month, recent years, and holidays).