Without searching I have no idea what that is supposed to mean. I guess it is something related to free speech in the USA? I might remember it from school.
What I am implying is that it seems like a localized term and people elsewhere might have no connotation(?) to it. In German the word means a curl of hair.
I'd say the advantage of 'Locke Mail' is that it gives the right associations even to people who haven't heard of John Locke. Locked Mail. Mail protected by a (cryptographic) lock.
He might be fitting in relation to US history considering that while he spoke of equality and freedom, he was a major investor in the slave trade (he also was involved in trying to introduce a feudal aristocracy in Carolina).
He was very progressive for his time, and so he's one of the "icons" of classical liberalism, but he died in 1704, and we've moved on a tad from then.
What I am implying is that it seems like a localized term and people elsewhere might have no connotation(?) to it. In German the word means a curl of hair.