The legend writ
The stain effected
The key in Silence undetected
Fifty-five in iron pen
Mr. Matlack can't offend
The Meerschaum Pipe was found by Ben Gates in the Charlotte. This riddle was engraved on the stem of the 200-year-old Pipe. Ben used his own blood as ink in order to read the riddle. Each line of the riddle refers to another clue, and together, the riddle points directly to the Declaration of Independence.
The legend writ: Refers to the legend of the Templar Treasure which has been passed down through multiple generations, and then falls to the ears of Ben Gates. This line also refers to the Ottendorf Cipher that is eventually found later in the movie.
The stain effected: Points to the fact that the map is invisible - the stain needs to be manipulated in order to get to the next clue (the Ottendorf Cipher).
The key in Silence undetected: The Ottendorf Cipher is the key to reading the next clue which was hidden in the Silence Dogood Letters. The letters were written by Benjamin Franklin for the New England Current when he was around 16.
Fifty-five in iron pen/Mr. Matlack can’t offend: This part took a little more thinking on Ben’s part to decode. Ben eventually came to the conclusion that the riddle was talking about the Declaration of Independence. “Fifty-five” is pointing to the fact that 55 men signed the Declaration at the time the riddle was made. "Mr. Matlack" is Timothy Matlack, Scribe of the Declaration of Independence.