The S.O.S. transmission received on the Ford's radio is in Morse Code. Morse Code would later be used in Season 7's "Drive" when Ensign Kim signals Lts. Paris and Torres of the Delta Flyer's sabotage.
Trivia: This episode sees the first ever use of a "Blue Alert", which is the signal given for a starship to land on a planet. This episode is also the first time in Star Trek history that a Federation starship lands on a planet and returns to space.
Trivia: It is established that warp 9.9 equals about 4 billion miles per second.
Trivia: Janeway states there are 152 crewmen aboard Voyager in this episode. This is the first time the crew is specifically numbered.
Goof: AM radio waves are susceptible to refraction by ionospheres, static interference, large structures with metal reinforcements, and has a maximum range in the thousands of miles. An AM radio would not be able to pick any sort of planetoid based signalling from the middle of space far from any solar systems like the truck in Voyager did.
(sitting at the helm)
Earhart: How fast?
Paris: Warp 9.9. In your terms that's about four billion miles a second.
Earhart: Think I could take her out for a spin?
Janeway: Maybe not. Let me tell you some of what happened after you disappeared over the Pacific. No trace of you or your plane was ever found in spite of a massive search. Over the years there was a lot of speculation about your flight, including the rumour that it was financed by the government and may have been part of an operation to gather information about the Japanese.
Earhart: Where did you hear that?
Janeway: It's somewhat common knowledge. You see, Japan attacked Pearl Harbour in 1941, drawing the United States into a massive world war. In retrospect, your journey was seen in a different light. Perhaps as part of an intelligence mission devised by a government deeply concerned about Japanese war plans.
Earhart: No one was supposed to know about that.
Janeway: Maybe not in 1937. Now it's part of history.
Earhart: I've been on expeditions all over the world and I've seen people do all kinds of strange things to their bodies. That doesn't mean that Martians have invaded Earth.
Kim: Actually, it was the other way around. Mars was colonised by people from Earth in 2103.
Janeway: I doubt there are many 20th century farmers driving around the Delta Quadrant.
The second season DVD release includes a text commentary ("special text trivia") for this episode. Included are factoids about the Ford Motor Company and information pertaining to the production of this episode.