In terms of seat reservations (where the same number is given to seats on opposite sides of a table) they are referred to as (e.g.) 14B and 14F. I've always interpreted this as 'Back' to direction of travel, or 'Facing'. Naturally this can be fun when the train reverses en-route.
This was the traditional arrangement, with opposite seats having the same number. I don't think it was ever done for face-to-back seats, referred to as airline and coded "A", so not only did you not get a table you also had a 50% chance of facing backwards!
EMT and possibly other operators have now abandoned this, with all seats just numbered singly. Since the orientation of trains on EMT is essentially random, even with a seating plan you don't even know which way you will be facing.
My late grandmother used to insist on "facing the engine". I think I did try to explain that meant something different on HSTs and 225 sets. She didn't live to see the Voyagers where she would have been lying face down on the floor...