This paper investigates manufacturer encroachment on a sustainable supply chain, where the manufacturer holds exclusive information on product greenness and is responsible for both corporate social responsibility (CSR) and greening. The manufacturer and the retailer play a signaling game whereby CSR effort and wholesale price serve as joint green signals. Findings reveal that, firstly, encroachment induces higher CSR efforts from manufacturers. When customers exhibit a strong CSR preference, the resulting CSR increment leads to increased offline demand and drives up both wholesale and retail prices in a mutually beneficial manner. This phenomenon is referred to as the CSR effect, yielding a win-win encroachment. Secondly, when signaling product greenness to highly CSR-sensitive customers, the high-greenness manufacturer principally distorts her CSR effort downward to an extent unprofitable for the low-greenness manufacturer to mimic and subordinately distorts the wholesale price downward to counter CSR-induced demand decrement and mitigate CSR cost pass-through downstream. Finally, the win-win encroachment pattern is characterized by encroachment profit and signal expense sharing, with encroachment strengthening downward-distorted signaling while signaling weakens the CSR effect. These insights contribute valuable guidance for green manufacturers in CSR decision-making, which functions as a component of green signaling and facilitates transitioning to dual-channel sustainable supply chains.