cafeastrology.com › whats-my-veWhat's my Venus sign? | Cafe Astrology .com For most birthdays, you don’t need to know your birth time to know your Venus sign. On some days of the year, however, Venus changes signs. If you were born on such a day, you will receive the message that Venus in your chart is in one of two signs. In these instances only, you will need to know your birth time to determine your Venus sign.