Just about all of the discussion about coded language in 19th century or earlier African American songs refers to escaping freedom.
I've written before my sense that this theme is overworked, and probably not applicable to every time songs like "Steal Away" and "Swing Low, Sweet Chariot" were song.

However, though this is a discussion about spirituals, I want to share my sense that some 19th century African American secular songs did speak indirectly, if not in coded language, about these peoples' ridicule of and dislike for their masters and mistresses, and the fact that they would not shed a tear when these people died. The most widely known of these songs is "The Blue Tail Fly/Jimmy Crack Corn". Of course, there are those who may think that this is not an authentic African American song which ridicules White folks so I'll also add the somewhat less familiar song "Master Is Six Feet One Way" which clearly ridicules "massa":

Mosser is six foot one way, an' free foot tudder;
Am' he weigh five hunderd pound.
Britches cut so big dat dey don't suit de tailor.
An' dey don't meet half way 'round

Mosser's coat come bacl to a claw-hammer p'int.
{Speak so' or his Bloodhound 'll bite us.}
His long white stockin's mighty clean an' nice,
But a liddle mo' holier than righteous.

{Source: Thomas W. Talley's 1922 "Negro Folk Rhymes", Kennikat Press Edition, 1968, p, 40}

Nowadays, people would call that a rip and say something like "Oh, snap! in appreciation of the put down. The important line to note is {Speak so'[softly] or his Bloodhound 'll bite us.} These people weren't foolish enough to go singing this song when "mosser" could hear it. {And btw, Talley emphasized in his preface, these were songs and not prose.} There were grave consequences for being that foolish. So "coded" songs, in this respect means singing obliquely about a subject, and being careful where and when you sang it.

In addition to including examples of secular African American songs that ridiculed White folks, Talley also included some songs that I think reveal the composer's discontent with slavery and his determination to fight to be free, even if it led to his death. Here's one example of such a song written in what I believe is coded language:

DIE IN THE PIG PEN FIGHTING
Dat ole sow sad to de barrer:
"I'll tell you w'at let's do":
:et's go an' git dat broad-axe
And die in the pig-pen too"

"Due in de pig -pen fightin'!
Yes, die, die in die wah!
Die in de pig-pen fightin'
Yes, die wid a gitin' jaw!"

{Talley, Negro Folk Rhymes, pg. 39}