Through the use of archive footage, Brains informs the team of a discovery - but in order to gather more information, our heroes split into groups and search for an escape pod missing since Jeff Tracy's crash.
- Scott Tracy, Alan Tracy - Rasmus Hardiker
- Virgil Tracy, Gordon Tracy - David Menkin
- John Tracy - Thomas Brodie-Sangster
- Kayo - Angel Coulby
- Brains - Kayvan Novak
- Grandma Tracy - Sandra Dickinson
- Lady Penelope Creighton-Ward - Rosamund Pike
- Parker - David Graham
- Colonel Casey - Adjoa Andoh
- The Hood - Andres Williams
- Havoc - Aimee-Ffion Edwards
- Jeff Tracy - Lee Majors
- Braman - David Graham
- Dobbs - Thomas Brodie-Sangster
- Reece - Vas Blackwood
- GDF Pilot - Kayvan Novak
John: "Without giving a reason why, I've convinced the GDF to turn off the laser protection system for 20 minutes. That should give you enough time to get in, find the capsule if there is one and get out."
Alan: "What if we don't find it in time?"
John: "Then you'll be the first Tracy to see what a 50 kilowatt laser feels like."
John: "I'm just kidding."
Parker: "You rang, Mr. Gordon sir... again?"
Gordon: "Parker, I was thinking, you know what would be really great right now?"
Parker: "A holiday?"
Gordon: "A milkshake. Butterscotch. Extra cherries."
Parker: "Extra cherries."
Gordon: "I could get used to this."
International Rescue Equipment Used
- Airing right after the SOS episodes, Signals marks the first time that multiple two-parter episodes have aired after each other. Indeed, with the revelation that Jeff Tracy is potentially still alive, the SOS serial leads directly into the Signals serial, effectively making these episodes a four-parter.
- However, an uncertain amount of time appears to have passed between the two serials, as Gordon has returned from the hospital (with some progress) and a new Thunderbird 4 has been built.
- Despite being obscured by an opaque helmet and only being seen in archive footage, this is the first episode to feature Jeff Tracy.
- This is the first time that Lady Penelope and Parker are seen on Tracy Island.
- The Zero-X spacecraft returns from the Thunderbirds Are Go film, only this time it now has an engine that is said to be capable of reaching speeds that are faster than the speed of light.
- Although described from the beginning as a "crash", the Zero-X incident is revealed to be a mid-air explosion, with no collision or impact.
- Scott pilots Thunderbird 4 for the first time while Penelope co-pilots Thunderbird 2 for the first time.
- As a cliff hanger for this episode, Havoc steals Thunderbird 3.
- This makes Thunderbird 3 the first Thunderbird to be seen piloted by anybody other than a member of International Rescue.
- Clips from the ending of Ring of Fire Part 1 are used in the pre-title sequence, plus clips from SOS Part 2. Unlike the ending from the previous episode, Kayo states "he may still be alive..." instead of Brains.
- This episode confirms that Kayo's father is still alive and never got over what happened to Jeff, indicating that the two were close friends. Kayo even mentions that if Jeff is still alive, it could bring her father out of retirement.
- It is stated that Jeff has been missing, as of the time of Signals, for almost eight years.
- However, an unspecified amount of time has passed since Ring of Fire Part 1, which is when the year was 2060, so the Zero-X incident took place sometime after 2052.
- This is the first episode in which no rescue takes place.
- This is the first time that Havoc appears without Fuse, and the first that either of the Chaos Crew appear without one of their three vehicles.
- This is the second episode that Dobbs and Reece appear in, the first being Ghost Ship. They appear once again in the second part of Signals.
- Adjoa Andoh is credited as Colonel Casey, rather than Captain Casey.
- Although it later turned out not to be the case, this episode was the first to show the death of a character (Jeff Tracy in the explosion).
- Although it isn't Lady Penelope who does it, Parker is called over by a bell, very much like his classic series counterpart.
- During the launch sequence, when the Space Elevator takes off from Tracy Island, Thunderbird 4 can be seen inside its own water tank when it should be aboard Thunderbird 2 (Module 4).