Currently, we have a little line at the very bottom when asking a new question as an unregistered user:
There is a similar line in small text when registering an account, almost hidden away.
These messages are easy to miss, and they are potentially not legally binding. (See also: "By posting this, you agree to our terms and conditions" - maybe other options are not legally binding either, but everything indicates explicit acceptance is always better.)
I propose that they are made more obvious, by moving them above the submit buttons, and in at least the standard font if not larger. Also, perhaps include a checkbox to confirm their acceptance. It is a minor obstruction, but potentially useful where a user wants their content deleted - it makes it harder for them to claim ignorance of the content licensing:
You agree that all Subscriber Content that You contribute to the Network is perpetually and irrevocably licensed to Stack Exchange under the Creative Commons Attribution Share Alike license.
(Yes, I am aware of the bit at the bottom of the page about the CC licence. It is still not very obvious to a new user posting a question or registering.)