What is some good boilerplate for a comment on a post that lacks citations or references? When you see a post that appears to be pure conjecture, not backed up by or referencing the source material, you should make a comment. I'm looking for a good example of a standard comment to use in this instance.
There are a couple of challenges with this that should be considered.
One is that it is often disconcerting to new users to get what they consider a reprimand on their first attempts to participate.
Another is that some people will respond by saying "nothing in your rules says I have to provide a citation/reference!"
I'd suggest something along the lines of:
This answer appears to be pure conjecture. While answers based off of conjecture aren't prohibited, this particular question would be best answered using specific citations or references. Please consider updating your answer to include any factual information you can find to back up your conjecture. This will likely improve your answer, and make it more likely to be of use to other visitors.
If the user in question is new to StackExchange (< 101 reputation), I'd suggest a simple "Hello, and welcome to the site!" be prefixed to the above.
Moderators can add a notice underneath a post:
This post does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
The notice feature isn't very useful because it doesn't even notify the poster and it is limited to three canned texts (citation needed, current event and insufficient explanation). We aren't in the habit of using it in SF&F because we don't consider the lack of citations to be damning (unlike, say, Skeptics). But you can take inspiration from the message.
Also, maybe we can get into the habit of using the post notice sometimes. It's in the mod menu under “add post notice”, and there's a mod tool to list posts with notices. Non-mods need to flag if they think a post notice is warranted. Note that I'm only mentioning the technical possibility here: if we start using post notices, we should have a separate meta discussion about when to use them.