Related: How can I cite a question in SE?
Math.SE has a citation tool. Basically, if you click "share" on a post, there's a little "cite" link:
Clicking that, you get:
This lets one properly cite a Physics.SE post in a document by the attribution rules.
Do we want this? While it may not be so useful for formal journal articles, I see how it could be useful for miscellaneous documents (remember, visitors can use it too).