After struggling with this issue for several weeks I have decided that from now on, I will add an exclamation point after "Thanks" in all future e-mail correspondence. It seems to convey more sincerity than a "Thanks" sans the exclamatory punctuation. I would like to apologize to anyone who may have received what they perceived to be a less-than-enthusiastic "Thanks" from me in the past. What I really meant was "Thanks!"
NOTE: A more formal "Thank you" will still be punctuated with a period, as in: "Thank you for your time." Emoticons are still off the table... for now ;)