What light should a vessel engaged in trawling display?

A vessel engaged in trawling is required to display two cones with their apexes together. This configuration signals to other vessels that the trawler is actively fishing and not making way, signaling the presence of gear that could pose a hazard. The two cones are recognized internationally as a specific indication of trawling activity and help ensure safe navigation in the vicinity of the fishing vessel.

The other options do not accurately represent the requirements for a trawling vessel. For instance, a green sidelight is typically used for specific navigation purposes and does not convey the fishing status. A single white masthead light is more indicative of a vessel under sail or at anchor rather than one engaged in fishing. Additionally, an all-round red light is used to indicate a vessel that is not under command, not one that is actively engaged in fishing operations. Therefore, the correct answer regarding the proper light display for vessels engaged in trawling is indeed the two cones with apexes together.