Japanese Naval Signal Flag #5—Code "Go" 最初の5の日本の海軍艦隊信号-名前「ご」

The Japanese Maritime Flag for the Number 5 is the inverse of Romeo.  It has yellow field with red cross.

Note that IJN #5 Aux Flag is the inverse of the Romeo-R ICS flag.

You can see the Go flag in use with IJN Coded Signals.  The Imperial Japanese Navy Auxiliary Number flags were used International Maritime Flags in the Japanese Navy.