Secret communication channels are only as secret as the people using them. Why go to the bother of intercepting and then trying to decode a ciphered message from the duke to the king when you can just kidnap the duke and hold him hostage until the king pays the ransom?
If you've never considered having nobles and high officials in your campaign send each other encrypted messages, try adding them in. And watch how your players creatively solve the problems that this causes for them.
Commentary by memnarch (who has not seen the movie)
Hmmmmm! And here we have one of the potential moles picking up a special trinket! Finn may or may not be working for the First Order, but I bet if this does allow for communication to Rey somehow, this could let them know where she's at. Encryption doesn't prevent seeing where the info goes after all! That wouldn't be like the Star Wars movies I can remember though. The one time that might have happened is probably the result of the Geonosian spotting the ship.
Wild guessing at the next comic plot twist aside, it's definitely an important bracelet. A) it's got the neat little blue glow, B) it's getting all this visual focus put on it, and C) Rey has one that looks pretty much the same. Also curious to note is that no one appears too concerned that Finn picked it up. Assuming the communication part is made up for the comic, that leaves its function as..... what. A sign that Leia trusts this person, that few people would understand? A very long shot, but if Finn stumbles his way into meeting up with Luke, that could be good for Finn. I'm pretty sure Rey isn't going to get Luke off of that planet any time soon, but maybe they'll end up meeting up there somehow? The map could have been copied I suppose
Also, man. It's been almost two months since we last saw the bracelet. It's funny that it feels less like it'd be a paired communicator now, though perhaps that's because it's been shown before and I don't see Finn as knowing that Rey is on the other side in the movie in this case.
GM: <roll> As Leia is antigravved away, her limp fingers drop the secret decoder bracelet.
Finn: I pick it up.
Finn: I can send a message to Rey using this?
Finn: And it’s secret?
GM: It’s encrypted.
Finn: Rey, I don’t know if you can hear this, but we’re being chased by the First Order and can’t throw them off.
Finn: Leia has been injured. And Allan died... but his triplet Edgar showed up.
Finn: His family sure has bad luck. They should consider a safer job. Like Imperial troopers.