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xkcd #3169: EPIRBs
(imgs.xkcd.com)
Title text:
'Oh no, the box is drifting out into the harbor!' 'Yeah, I wouldn't worry about losing it.'
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3169/
It's been a while, but off the top of my head: MMSI (which is basically the radio installation identifier. Same number is used for AIS), and an ID digit (0 in wheelhouse, 1 on starboard bridge wing, 2 on port, etc)