No, because GIFs in the body of an e-mail do not animate in Entourage.
However, if you send the GIF as an attachment, the recipient should be able
to open it in another program if it doesn't animate automatically.
The simple rendering engine in Entourage does not animate gifs, however
there are tricks to make this happen in the body of a message.
Unfortunately, they won¹t work in a signature.