This is a questions which has been asked on Reddit after the landing at night of the booster used in JCSAT-14 mission, however no one has been able to provide a valid reason. The lights in question can be seen here or in the video, right after the landing. They appear to be steady-white for about 30 seconds, after which they began to blink.
Some possible explanations included:
- FAA regulations (but the rocket operates in a no-fly zone, and the legs are opened just seconds before touchdown)
- Naval regulations (but they could have attached lights after the landing and avoid the weights - if the lights from the barge were not enough)
- Safety lights in case the rocket would splash down, but it's highly probable that it would sink in this case
- Safety signaling for the crew, but the use of telemetry data makes more sense for that