This question already has an answer here:
For duplicates that cross main sites, there exists this question. However, I think the rules might be different for meta. Is there a reason for not allowing cross-site duplicates on meta?
meta.SO seems to be the central point for certain Stack Exchange things, such as general policies. So, when a question like this one on Arqade meta comes up (or the same thing on mathematics, server fault, and super user), it would be nice to mark as duplicate of this meta.SO question. At the very least, if "linked", the cross-site duplicates should probably show up in the sidebar.