I'm alert enough to notice that few passengers will attempt to sit next to ANYONE if there is an option. If they can find a seat or a table where they're likely to be alone, that is what people tend to do. This has also included people that they are traveling with. They'll sit across the aisle from each other, with their belongings against the window seat. I'm also alert enough to know that this is a public forum (in this case, transportation) and I don't need to feel "invited" or "welcome" to take a seat...that I paid for. The same sign or message that often occurs when a passenger is looking for a seat and they see another person is occupying two seats with personal belongings or their feet or sleeping across multiple seats, in a packed train despite multiple announcements advising "the train is sold out and please make all seats available...there are people looking for seats". People will often attempt to avoid saying something but when they run out of options or they want "that" seat, they usually say "excuse, is anyone sitting here?" or if the space is empty, they'll merely sit down. Papers on the tables would mean very little to me. The only way papers would dissuade me is if they were actually on the seat. Now, if there is food on the table, that is a different story. Perhaps you are talking to the wrong people or your wish to avoid a confrontation (I wouldn't have guessed) made you feel "uninvited?" My personal experiences don't lead to confrontation or me standing. They lead me to saying "excuse me", is this taken" or "excuse me, are you using this batting cage" or going right to someone's dinner table at a pizzeria and asking "Are you done with the oregano shaker? Yes? Good...I can put it back with the rest of the condiments if you'd like." Somehow, when it comes to strangers in public, I've never felt the need to feel invited But, not everyone is me. That being said, the crew is allowed a work space. On trains without crew quarters, they should use general seating. However, if general seating is sold out, they are allowed a work space in the cafe car. "A" table. Not two...not three. They are allowed 1 table as a work space. That does not mean they are confined to one table. Neroden said it best when he said they may not monopolize the tables for work space. If they do, it is definitely not allowed and if for some reason someone DID say you can't sit with them, definitely get names and report it. Immediately.