I was chatting when I accidentally placed % instead of ^ in between brackets. What I found was a hidden emoticon that's not in the list of normal emoticons! :P

Try it. Type (%) while chatting.

Hehe! Quite nice!

Ps. It was tested in WLM 8.1.0178

EDIT:

I find people are quite interested in this post, and decided to add some more material here. I found that other hidden emotes exist, and a list can be found here.

There's also the I'M initiative which has its own hidden emote. More info here.