Answer:
A paradox contradicts itself. So, the posted sign that orders people not to read it is a contradiction in itself.
Explanation:
A paradox is when any logical statement or sentence contradicts itself. By posting a sign that orders people not to read it, it is contradicting it's own logic. What was the purpose of posting the sign if no one should read it? So, when the sign orders people not to read it, but was still posted, then it becomes a paradox. If the sign wasn't to be read, then it should not have been posted in the first place. For, signs posted are meant to be read.