The Roman god Luna
Roman gods are shown with instruments of their power, Neptune with the trident, Jupiter with the lightning bolt. The horned head crescent is a symbol of a solar eclipse. This demonstrates Luna's greatest power, to dominate the sun during a solar eclipse. Solar eclipses are difficult to symbolize for ancient cultures. Looking at it for brief moments may result in permanent vision loss or blindness, adding to the associated fear and terror with the event. Note the moon is black and ancient uneducated populations would have difficulty drawing this. The solar crescent is actually a double crescent in a three dimension sculpture. Imagine viewing a solar eclipse and the double crescent is solar. The upper crescent is on a slope because it slides the moon on the solar crescent before obscuring the sun. Note the reverse male-female anatomical implication with Luna and Sol. Other double crescents show the lunar crescent above the solar crescent in an additive effect during a solar eclipse.
Horn up lunar crescents are called "wet moons" and are named so from Pacific island cultures. They are more frequently seen in equatorial latitudes. To say the above crescent is strictly lunar would be akin to saying Neptune is the "god of the trident" and is superficial to the intended meaning. Unlike current western theological and political attitudes, Roman gods were to be feared and respected as was the Roman emperor. These images and sculptures were meant to reinforce this fear and terror.
The crescent of Our Lady of Guadalupe is double and additive. The moon crescent and solar crescent compliment each other and are not depicted in the Roman fashion. Domination, fear, and terror were the main elements of the Roman world. The Judeo-Christian world emphasizes love, compassion and cooperation. This only came with the sacrifice of the Lord Jesus Christ.