When you're copying the code, you need to make sure you have the HTML version so trying grabbing the other choice of code from this site. Once you have the code, make sure you check the Use Your Own HTML tags under the box in your board settings before you paste it in there. Press submit and it should show. Let me know if this doesn't work.
Also, You might find some useful information here: Creating a Message Board Signature
KarlaCommunity Moderator, iVillage.com