This study investigates a supplier’s channel encroachment strategy on a retail platform under asymmetric demand information. Within a two-echelon supply chain consisting of a supplier and a retail platform, we develop a signaling game model and examine three supplier strategies: no encroachment (using the platform only for distribution), committed encroachment (pre-committing to a consignment quantity before the platform places its order), and delayed encroachment (determining the consignment quantity after observing the platform’s order). The results show that when the platform’s commission rate is low, the supplier prefers encroachment. When commission rates are low and market fluctuations are small, delayed encroachment emerges as the optimal strategy. In other cases, committed encroachment is preferred. However, relying on the platform’s order quantity as a demand signal is not always beneficial. When fulfillment costs are high or demand variability is low, disregarding this signal yields greater advantage for the supplier.