I've seen this on the wall-facing side of many (North American) AC power connectors.
What is it called?
What does it mean?
Electronic – What does this AC power connector symbol mean
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Related Solutions
MXJ means the connector was made by Molex, in Japan. If you measure the exact pitch, then look on the Molex website for connectors with that pitch, you can hopefully find the appropriate mating connector for your application.
I pulled this from a random Molex shrouded header datasheet:
Notice "TRADE MARK" notation on the center-left.
It looks like a solder bridge. Sometimes there can be a jumper that you need to put, sometimes it is just two very close pads that you join with a blob of solder.
Best Answer
It's a kind of datecode. The mold for the plug actually has a small part that can be rotated with a screwdriver, to point the arrow at different numbers around the perimeter of the circle. They do this to either indicate a new month of manufacture, or perhaps a revision number.
Note the 1 and the 3 on either side of the arrow. In this case, it's a datecode indicating the third month of 2013. Once a month, they rotate the arrow, and once a year, they replace the rotating part altogether with one for the next year.