The sprite for that power-up box is apparently tucked away in the game data (because I've seen it on multiple sprite sheets) but I have never seen it in the game. I have no idea what it's supposed to do, so I came up with an idea.
As I explained in an earlier comment, I did not know what the intended effect of the power-up was, because I had never seen it in play before (I never played S3&K in debug mode). In my sprite sheet of game items I found three S-monitors: a blue one like you mentioned, this red one, and a reversed blue one.
And doesn't the shoe power-up also make your character hyper? If so, why the two kinds of power-ups?
Yes, their brains got switched. I was planning to make that more clear in the next comic.
I did contemplate the idea you said. If I used tails on my talk bubbles, then I could do that, but since I position the bubbles so that they're read in the intended order and not necessarily near the person speaking, it'd be hard to follow.
Just so you know, If you use the blue monitor in debug mode, you instantly became Hyper Sonic, Super Tails or Hyper Knuckles and gained 50 rings in S3&K. In Sonic 3 alone (without S&K) or S&K alone (without Sonic 3), that monitor was red and could turn you into Super Sonic or Super Knuckles (there is no Super Tails without the super emeralds upgrade) in debug mode. As for the reversed blue one, I've never seen it.