Well Navy ships only have the writing on the front side of their sails, not on the back - atleast not in the ships they sent after Mihawk/Buggy. It could be both imo, not just strictly WG.
But yeah, I don't think Oda has any plot/narrative purpose for the BMP this arc - he used them as an hypetool for King and Marco already. It's probably going to be used similarly for the force that's invading Wano now.