I think a simple "Honor System" applies here.. You need to be the one signing the log, to log the find online.
The idea of signing a log for everyone in the team, including the ones in the car a mile away, the rest of the team still stuck in work any variable distance away, the one serving in the armed forces clear across the planet, The team member who's an astronaut aboard the space station, etc... You can see how ludicrous this could go..
Simple stated.. If it's a team find, EVERYONE in the team MUST sign their OWN signature, if they want to log it online.
Though, I've got a couple of caches, where someone signed the log book, but never logged it online.. Go figure?
Are you serious!? My bff and I ALWAYS cache together and we both have "jobs". She signs the logs while I write the cache name and any notes in our personal logbook. I don't understand why this is wrong...