Samuel L. Jackson on one side.
His wisdom, “Spend it wisely, muthafucka” on the other.
Are you talking about the hidden lower-case L? I had to use that because the board won’t let you post all upper-case letters.
Unfortunately they keep less than $100 in cash on the premises. 
Hm?
Uncle Sam decked out like a gangsta rapper - baggy pants, big dollar sign hanging from a chain around his neck, garish sunglasses, with his hand up to his face making that universally known Vulcan death grip-like gangsta gesture.
On the back it’d say “One Trillion Dollars, Mothafucka.”
Co1n?
Obama’s face on one side.
“Change we can believe in” on the other.
“THlS” with a small L instead of capital I.
I didn’t notice it either.
Win. 
I’ve been wondering how big this coin would be. The Royal Canadian Mint actually created a one-million-dollar gold coin a while back; it’s the size of a manhole cover and is made of 100 kg of fine gold. (They sold several.) So, would a trillion-dollar platinum coin be bigger? Covered in fine gems? Engraved with plutonium-plated holograms? Or would they take the other tack and make it inconsequential-looking, such as dull-grey and smaller than a dime?
100kg? Chump change. Make the trillion out of a cubic foot of gold = 1,200 lbs. Crust it up with plutonium, diamonds, hell, have it hand engraved and burnished bright as the sun.
It should just be blank, with a symbolic bullet hole through the middle of it.
A picture of Confucius and “100 yuan”
With the idea of a trillion dollar coin being kicked around again, I thought I’d revive this thread.
Anyway, I kind of liked Stephen Colbert’s idea: