So when it's your zodiac sign year, you are supposed to wear red underwear for good luck. When you walk through the shopping mall, you will see lots of red underwear on the mannequins in the windows. I couldn't find my size even if I wanted red underwear, because Chinese are very thin. But I am slightly obsessed with the red socks. I have been buying them to give away, and even kept a pair for myself, but I haven't tried to see if they even fit. But they all have embroidery on the side, that usually is the character for blessing.
The character is upside down because Chinese look at this character kind of like we in the West look at lucky horseshoes. They hang it upside down so the luck won't run out. :) I guess it also helps so that when you are looking down at your socks, you see the character right side up. ;)