Did some quick and dirty investigations various games preceding Spitfire.
The Channel F built-in games have graphics for the charcters 0 though 9, G?TMX-:, and various slanted lines. I’ve done enough looking at the code in the past that I’m confident this game doesn’t have a secret message.
Also, various carts use graphics and functions from the built-in games. If those games don’t have additional letters of their own, I’m going to assume they don’t have secret messages either.
Videocart 1 is a multicart with 4 (four!)
games pieces of software in it. Tic Tac Toe has a bitmap font that includes the following characters in this order:
Using that as a text table in a hex editor reveals that the game has 5 (five!) strings in a length-string format. All of the messages are used, although the -, C, and H in the font appear to be unused (in these strings, at least).
Length: 15 - _______________
Length: 10 - YOUR_TURN!
Length: 8 - YOU_WIN!
Length: 15 - YOU_LOSE_TURKEY
Length: 10 - ITS_A_TIE
(Yes, the game really does have a 15 character blank string. It appears to use it to undraw the text.)
(Also, yes, that is the game’s real loss message.)
The other three games on the cart don’t appear to have any notable graphics of their own.
Videocart 2 reuses the Shooting Gallery game from the previous cart, and that doesn’t have anything interesting. Desert Fox only has tank and playfield graphics, so I doubt it’s hiding anything.
Videocart 3, Blackjack, has some letters:
(Yes, a bitmap of the letter T is really included in the game 4 different times.)
The graphics for cut, hit, and bet are stored separately from the rest of the graphics, and each of those words is preceded by a byte that appears to determine the word’s color. Thus, it is unlikely those letters would be referenced by a string elsewhere.
As far as the other letters, I doubt they’re used for a secret message.
The Atari 2600 was released in September of 1977, months after Spitfire, so none of its games would qualify.
The RCA Studio II, however, debuted in January 1977, which means it (probably) predates Spitfire.
Taking a quick look at some of its games, I’ve noticed two things: (1) viewing the graphics in YY-CHR still works, and (2) aside from the built-in set of games, most of the games are half or a quarter of the size of a typical Channel F game (1 kB, or even 512 bytes). Nothing immediately stands out from what I saw. Maybe somebody familiar with its assembly language would know better.
As for dedicated Pong and Pong-like systems (1st gen stuff), I doubt they’d have any secret messages able to be seen by the end user. However, I think it’s very likely for that at least one of them has something whimsical or personal etched into the silicon itself. That research, however, is outside of my purview (who wants to decap antique electronic chips?).
Beyond that, there’s still several dozen video arcade games predating the Channel F Spitfire, and quite a few mainframe/terminal-based computer games. These kinds of games are not as well-documented as home console games are, and quite a few games from this era are lost forever (as far as anybody knows). Any of those games could be hiding secrets.
In conclusion, I had Quadra-Doodle from Videocart 1 running in the background as I was writing most of this post. This is what it looked like after an hour or two: