Not really. The principle in play is "We're all adults; don't be a dick."
Proper etiquette would be to ping the meeting organizer and ask if they mind if you sit in. If they don't, no problem. If they do, you work something out relevant to the reason you wanted to sit in. But one can't even start that conversation without knowledge of relevant meeting topics.
The fact I know what meetings my coworkers are having doesn't imply I should be crashing them any more than the fact I can see when my coworkers are at their desks implies I should be continuously bothering them.