Can/should one put a copyright notice on one's CV or resume? Why/why not? I have not yet seen anyone in academia put a copyright notice on their CV or resume. Why is this? 

One might expect that even if the content is implicitly copyrighted, the layout/format/style of the document -- perhaps more so for a graphic designer -- is part of one's intellectual property.
While your CV can technically be regarded as a piece of intellectual property, the usual reason why people assert their copyright to a work by putting a copyright notice on it is to deter and prevent other people from copying or sharing that work (usually so they - the authors - can profit by selling the work). 

With your CV, it is actually in your interest to have as many people as possible sharing it and passing it around, so the incentives work completely in the opposite direction from a more traditional type of intellectual product.

Now, if your CV is such an amazing piece of work that people will be willing to pay for a copy, we’d be having a different discussion...