According to Dr Karl:
And in 16th century Naples, in Italy, kissing was an offence that carried the death penalty.
Is that true?
That exact phrase is repeated numerous times on what appears to be thousands of web sites. However, in the 50 that I took a look at, none of them sourced it. The best I have found is reference to a law passed on March 9th, 1562. Apparently an anti-obscenity law. As to how strictly it was enforced, I again am only getting references to the law itself (without any actual text of the law).
Given this pattern, I would suspect that perhaps an anti-obscenity law was passed on that date in Naples, but it was not strictly aimed at kissing, but other behaviour deemed immoral by the local magistrates/clergy/rulers. Kissing was just one thing mentioned.
I will continue to search for the original text of this law, but History is not my greatest subject, so I am leaving this as a wiki for the community.
The book The Kiss and Its History, translated into English in 1901, says:
The question of kissing by main force can be treated not only from an ethical, but also from a juristic point of view. Holberg relates that in Naples the individual who kissed in the street a woman against her will was punished by not being allowed to approach within thirty miles distance of the spot where the outrage had taken place