Here is an interesting patriotic cover, which is a bit busier and more detailed than most I've seen (though granted that number is not a large one.) This link provides a larger version that may help you see the details better.
This illustration shows Uncle Sam on a picnic sitting on a bank, with a picnic basket marked "Union" next to him. Both appear to be sitting on a United States flag.
Uncle Sam is saying" Here's the bait" as he holds a fishing pole out over the water, with the United States flag apparently serving as a floater and a cannon in the water as the hook. In the background the sun is setting, with the words "Our Union" among the suns rays.
In the water, entitled "Secession Pond," await a few fish and other water creatures. The one at the top, halfway in and halfway out is Kentucky. This may be a symbol of Kentucky's attempt at neutrality - not fully in the secession waters, but not all out of it either.
Swimming deeper are fish called "NC" (at the far right), then "LA" just left and below of NC. "SC", which seems to be in the shape of a puffer-type of fish (is this a reference to South Carolina's reputation as the "fire-eater" and most aggressive of the southern states?) is the one in front of the cannon, while immediately below it sits "Texas" in the shape of a snake or eel.
The large one below the cannon is "VA."
Another eel-like creature lies on the ground below Uncle Sam's feet, and is known as "Maryland."
On the bottom of the picture, on the land, is a longer snake-like creature, called "Secession" and below its open mouth are the words "out of breath."
The only other text on the envelope states "Copy Right Secured by BERLIN & JONES 134 William St N.Y.' No copyright date is apparent.
I honestly am not sure how to interpret this one, though it obviously is a pro-Union, anti-secession piece. On one hand, it looks like it is saying the sun is setting on secession, and the beached serpent appears to show that secession is dying.
On the other hand, why is Kentucky pictured halfway in the water? If this was late in the war the Confederacy was nearing defeat, Kentucky had already abandoned neutrality. Then again, maybe this was a very optimistic early-war scene and the artist thought that secession was not going to last very long.
I also refuse to deny the possibility that this cover has some obvious meaning that I'm totally missing.
Whatever its meaning may or may not be, this is still an interesting image with great detail in it.