A Block next to an entrance/exit is actually a regular block or a superblock that has an extern element at the entrance/exit side to which it’s interacting. This extern element is part of a list of such elements belonging to one “extern group”, which in turn serves as destination and incoming source for train schedules.
Such blocks are considered shared between your district and that of your neighbor, therefore you and your neighbor need to coordinate how trains are to pass through. The exit symbol on your side represents the exit signal on your neighbor’s side for the train to continue to travel, although the status of that signal is not shown on your side.
The block itself does not have any attribute or property to indicate it is located next to an entrance/edit.
Note: between the block and the extern there me be a control point linked between them. This control point cannot have home or switching signals, but is used often to place a trigger (buzzer alert).
The above applies also to virtual entrances/exits, where trains come in on a random basis (i.e. not based on a schedule declared in CTC), and no exit symbol is displayed.