That’s not a license plate number: it’s the LDP’s cryptic way of tying themselves to the paternity leave system. Read out loud, it sounds similar to papa ikukyu (パパ育休) or “Daddy Childcare Leave.”
The code makes a very subtle appearance in the recent TV commercial featuring Sadakazu Tanigaki’s ridiculously impassioned speech about making Japan number one again. This spot has been coming up once in the rotation during every World Cup game I have seen so far (except, of course, the ones on NHK).
The slogan appears on the green silicon bracelet he’s wearing.
You can buy your own here, although you have to register as an LDP merchandise customer first, and I’m not sure whether non-citizens are definitively eligible for this. They do specify that you have to be a resident of Japan and that they will only ship within Japan.
(Thanks to Mrs. Peter for the tip)