any page under https://siggraph.org/* only shows homepage
The front-end of the website clearly isn't properly implemented to work over https. It still contains elements that can only be delivered over the unsecure protocol http. This results in the homepage not being properly formatted.
However, even worse is the fact that every page via https just returns the homepage. For example https://www.siggraph.org/ and https://www.siggraph.org/publications/ return the same page.
Other websites might link directly to a paper hosted on siggraph in pdf format and users will, leaving this ruleset active, be unable to view such pdf files. Try for example: https://www.siggraph.org/publications/poster-example1.pdf http://www.siggraph.org/publications/poster-example1.pdf