To remove factory emblems, I use dental floss and Goo-gone. Wait until its warm (or carefully use a hair dryer) and pull the dental floss back and forth behind the emblem, through the adhesive. Fishing line works well too, but floss is cheap and my car likes the mint flavor.

Once you get it off, the Goo-gone and a paper towel will take off the remaining adhesive. I like the spray gel of Goo-gone as it likes to stay where you spray it (nice when working on a vertical surface).