Which of the following is NOT a specific vessel identifier mentioned?

The correct choice of "D" indicates that 57301 is not a specific vessel identifier mentioned in the context of the question. Vessel identifiers, often used for tracking and communication, typically follow specific numbering systems established by maritime authorities. These identifiers can include MMSI numbers, IMO numbers, or USCG vessel documentation numbers, which usually have certain characteristics or formats that they conform to.

In this situation, the other choices, which are 47299, 47290, and 29233, fit into the established formats or patterns of vessel identifiers recognizable in maritime operations. Meanwhile, 57301 does not conform to the expected number patterns or ranges associated with vessel identifiers typically referenced. The lack of recognition for 57301 signifies it is likely not valid or relevant in the provided context, making it the correct choice for the question of which is NOT a specific vessel identifier mentioned.