Does anyone know what the three red lines in this architectural diagram mean?

It is neither "shear resistant" nor "encrypted", but "additional stirrups". This is a structural measure to deal with local uneven stress at concentrated loads. It is a structural measure stipulated in the concrete structure design specifications. There are no less than three structural measures with a spacing of 50mm. They must be equipped without shear calculation. Of course, it goes without saying that it can also bear a little shear force.