I asked my friend who speaks Chinese and he wrote it out for me - 精忠照赤日，大我贯青天
He said it's quite difficult to translate because it's a metaphor. The first part is a metaphor about the sun and the second is about the sky. His best attempt was that it basically means something along the lines of "I will endure suffering to bring honour to my country". He said the person who wrote is trying to show their humbleness.