TIL that there is a property called "brand_safe" in the json response for a subreddit post.
The following table shows which subreddits are "brand safe" and which are not.
As far as I can find there are no references to this in any of the (available) reddit source code. I wonder who is in charge of determining what exactly is "brand safe"?
If you want to see for yourself if a sub is "brand safe" simply plug "https://www.reddit.com/r/(subreddit here).json" into something like onlinecurl and search the result for brand_safe.