Signup form placed above content

I'm not familiar with theme development, so my apologies if I've misrepresented this as a bug report.

I am using the Signup module to enable signups for nodes. When implemented on the Sky theme, the signup form is appearing above the body content in the node view. On other themes I have experimented with, the signup form is placed below the content body, which seems to look better and more intuitive.

Would it be possible to update the theme, or alternatively, tell me how/where I could make the change myself?