https://www.pixiv.net/search.php?s_mode=s_tag_full&word=ワレアオバ"This is Aoba"
It's a historical reference. Specifically it's the identification signal mentioned in this paragraph:
>At 23:43, Aoba's lookouts sighted Scott's force, but Goto assumed that they were Jojima's ships. Two minutes later, Aoba's lookouts identified the ships as American, but Goto remained skeptical and directed his ships to flash identification signals 「ワレアオバ」. As Aoba's crew executed Goto's order, the first American salvo smashed into Aoba's superstructure.https://en.wikipedia.org/wiki/Battle_of_Cape_Esperance#ActionOops.
Aoba is cute.
