From what I've read, you can used taped games and software to decode the signs. That's not against the rules. Then in live games, if you're man on second (or anyone else who can see them with their natural eyes) can tip off their team to the coming pitches.

Where the Astros went wrong was using that information in real time, with a live feed to tip off their players (via trash can banging) whether it was going to be an offspeed pitch or not. That is breaking the rules (technology assisted) and they should have been punished IMO.

But to think that this isn't going on at all levels of baseball to some degree or another is just naive. It's practically as old as the game itself.