Paper money is actually extremely detailed and contains “microprints” that are not immediately visible to the naked eye.
The $5 Bill
Along the left and right borders are the words "FIVE DOLLARS".
There's an "E PLURIBUS UNUM" at the top of the shield within the Great Seal and "USA" repeated in between the columns of the shield.
On the back, "USA FIVE" appears along one edge of the purple number five.
The actual Lincoln Memorial has state names engraved on it, which also appear on the back of the bill.
The $10 Bill
"THE UNITED STATES OF AMERICA" and "TEN DOLLARS" reside below the portrait...
... as well as inside the borders of the note.
"USA 10" is repeated beneath the torch.
The $20 bill:
There's a "USA20" along the border of the first three letters of the blue "TWENTY USA" ribbon, to the right of Jackson's portrait.
"THE UNITED STATES OF AMERICA 20 USA 20 USA" appears in black in the border below the Treasurer’s signature (there's also a "20" between the two and zero, and "USA" in the circle of the zero).