As a letter closing, "Kind regards," That because it is basically a sentence with a lot of its parts emplied, as in "I submit the above with kind regards for you," in which the main parts of the subjective and objective phrases are easily interpreted by the reader without being spelled out. As a title, "Kind Regards" is correct, and it should be fine as a complete message (such as might appear on the front of a folded greeting card) as well.
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