yea, the Byakugan spots it with its wide range of vision.How does the signal get to Hinagiku? Does the byakugan see them? Whether or not Kiro understands what it says makes no difference. He’s trying to figure out how the information is transferred.
It's like leaving a note on the ground. While that might not be an effective means of communication for another Shinobi, with the Byakugan they'd spot said note pretty quickly.