What remark is appended to the report to indicate that the observation was not transmitted long-line?

The remark that is appended to a weather report to indicate that the observation was not transmitted long-line is "FIBI." This stands for "Flight Information Broadcast - Interrupted" and serves as an important signal to pilots and other users of the weather data that the transmission may not have been fully delivered or that there was some sort of disruption that could affect the reception of the information. This remark alerts users to the potential limitations of the data they are receiving, ensuring they consider it when making decisions based on that observation.

The other options either relate to different aspects of weather reporting or do not serve to indicate any interruption in long-line transmission. For instance, "SPECI" denotes a special weather report that provides significant updates, while "LAST" and "NOSPECI" refer to specific conditions of routine or special reporting, but do not convey issues with long-line transmission.