In scene 5, Blanche discusses astrological signs. What sign does she think Stanley was born under and why? What sign does she say she was born under? What does it mean?

From the text:

I bet you were born under Aries. Aries people are forceful and dynamic. They dote on noise! They love to bang things around! You must have had lots of banging around in the army and now that you're out, you make up for it by treating inanimate objects with such a fury!

Blanche is alluding to Stanley's forceful personality and physical behavior.