Here's a thought that seems to work in Europe. There are broadly three classes of train when it comes to reservations:-
1) No reservations possible.
2) Reservations recommended.
3) Reservations compulsory.
In 1) & 3) it is fairly simple as everyone knows where they stand (or even sit).
2) is the "problem" as very often there are no labels or displays, however, the expectation is that you will make a reservation, which you pay for, and this trumps any display. The onus is on the passenger "squatting" to prove he has a right to the seat otherwise he will have to move. Reservations are generally available up until a few minutes before the train departs - even from intermediate stations.