Daniel looks at an old newspaper and says it resembles an ancient Celtic text he found in Wales. The Celts, and Picts, used Ogham for all writing. Most Ogham letters are combos of straight upright and horizontal lines. Think of the hybrid love children of Ts, Fs, and Ls. The paper is clearly in a Gothic form of the Latin alphabet.
When Senator Robert Kinsey storms out of the Gate Room after Major Carter returns, Col. O'Neill tells Kinsey, "That's O'Neill... with 2 L's!", which he 'expresses' by holding up his first THREE (3) fingers; thereby asking Kinsey...and us the viewer...to 'read between the lines'. ;)
After O'Neill and Carter return from their first round of negotiations with the Aschen they are in the control room with General Hammond. They are talking about the note that was sent through the Stargate from Col. O'Neill from the future. In the background Sgt. Walter Harriman is holding and assumably drinking from a bottle of Pepto Bismol. Easy to determine from the shape and color of the pink bottle. It must have been a rough day of shooting.
The trivia item below may give away important plot points.
The newspaper which reveals the Ashen's crime is written in a subtract-one cipher: by moving each letter back by one in the alphabet, it becomes English. As Daniel Jackson says, the headline is "Vaccine from newcomers causes sterility", and the newspaper is called "The Volian Voice". Also, the same code is used in the name of the computer in the movie "2001", and thus the H.A.L. computer is code for I.B.M.