woollen cloth
旃 refers to a type of woollen cloth or fabric, often used historically for banners or garments.
旃 combines 方 (a flag or banner) with 丹 (cinnabar, red), suggesting a red-dyed woollen banner or cloth. The exact historical development is uncertain, but the components point to a textile associated with flags.
Picture a red (丹) flag (方) made of thick woollen cloth waving in the wind.
For セン, imagine a woollen cloth costing one hundred (百, ひゃく) sen (銭, せん) — an old coin — tying the reading to the idea of value: sen -> セン.