I would like to purchase but I am having a porblem seeing where I can sign a message using coinbase. Does anyone have any suggestions on how to do this?
-J
AFAIK You cannot sign a message using coinbase.
I would suggest you transfer your coinbase coins to a wallet you can control. I recommend the Software wallet Bitcoin-QT only because I use it. But there are other options such as web based or mobile phone wallets but there are some elevated security risks with those.
Here is a link to relevant material.
http://bitcoin.org/en/choose-your-wallet