These rules pertain to injection and MiTM attempts on your network connection.
Initially the rules were derived from a project I undertook when I observed when my ISP deployed a system to conduct MiTM attacks against it's customers to inject corporate messaging into web pages (more detail on this can be found at: http://blog.squarelemon.com/blog/2014/10/29/corporation-in-the-middle/ (SecTor) and http://blog.squarelemon.com/blog/2014/12/29/bsides-toronto-video-and-slides/ (BSides Toronto))
Although these rules were derived from a specific attack type used by my ISP, I have attempted to write them generically so that they can apply to other implementations of MiTM attacks (with one notable exception, which is specific to the product being used - however this device is in wide deployment so it is probably still a valid rule).
Since then however this started to grow as I discover other interception techniques for which snort/suricata rules can be written. This now includes rules for Superfish (http://blog.squarelemon.com/blog/2015/02/20/superfish-detection/) and Privdog (http://blog.squarelemon.com/blog/2015/02/23/privdog-detection/)
Added 3rd March - GeniusBox Detection (another install your own cert MiTM company like SuperFish and PrivDog). Relevent blog post with more details to follow.
These rules are written based on my personal observations an deployments. Feedback from others who deploy these rules (both positive and negative) can help to improve them. I can improve against false positives and can mark rules as "good" with validation from others. Please feel free to give me feedback either via github or twitter (https://twitter.com/synackpse).