Dan McCall's original design of Libertas, the Roman goddess and personification of liberty, which the Statue of Liberty was based from as well as numerous state seals and statues on the top of capitols.
Here Libertas holds the Constitution in her right hand with a shield (the defence of the Constitution), and her traditional spear in the other which is always vigilantly ready to strike at tyranny.
The hat she has on may look familiar. It's called a pileus, and was worn by Roman slaves after they became free. At her feet is a rattle snake, which is always ready to strike at those who look to harm Libertas. The rattle snake was a popular addition to Libertas when the Republic was very new, but has for a long time been left out of images of Libertas.