It’s actually an earlier mark, that of Debain’s grandfather, FranÃ§ois-Alphonse Debain. It was registered on 15 Jan 1847, renewed on 19 Jul 1851, and cancelled on 27 May 1864. The device — “un nacelle et deux petits hommes” [“a skiff with two little men”] - was also used in the mark of his son and successor, Alphonse-Edouard Debain in his partnership with Louis-FrÃ©dÃ©ric Flamant, working as Debain & Flamant, 1864-1880. The firm was succeeded by Flamant’s heirs as Flamant & Fils, 1880-1891.
Alphonse-Edouard Debain’s son Alphonse, however, became the successor to nearby silversmith Philippe Berthier, whose mark since 1847 had been “PB” with “un bÃ©casse” [“a woodcock”], hence its appearance in his Alphonse Debain’s mark, 1883-1911.
Hope this helps!