Here you go...
Reply with quote to this note, and they grab the first link (the one that ends in gif). You can paste that just like your siggie.
I would turn it into a proper siggie for you, but I don't know how to work with moving images. The fish one I found on the internet and did not change. Some peeps here have software to take that gif and add text around it to really make it cool. You could "go fishing" for tech help in the OT Help forum.
good luck!