A draft style guide has been added for SIGCHI, primarily to format headings, paragraphs, captions, and lists. The references are currently set to use the same style as IEEE. We will be updating the references during January 2016.
There is also a 'Project Template' available for projects according to the style set down by SIGCHI for conference papers.
Add these to 'My Styles' or 'My Templates' by clicking the open star. When you start a new project they will be in the available list.