Sterling or plate

Hello. I found a “Black Starr and frost” serving tray? I cannot find any info on silver plate items from this manufacturer. Did black Starr and frost produce silver plate? That’s the only mark I see. I don’t see Sterling or plate. It just says “black Starr and frost”

Black, Starr & Frost are noted here as making electroplate as well as sterling. The general rule for US pieces is: if it doesn’t say “sterling” then it most likely isn’t.