币

Bottom cloth radical (Kangxi #50) — pictograph of a piece of fabric hanging down. The indexing radical of 币. In antiquity, silk and cloth were money — exchange tokens before metal coinage. The cloth radical preserves that origin: 币 was originally bolts of silk used as currency in tribute and trade. Same radical anchors 帐 (account-book/curtain), 帆 (sail), 帝 (emperor).

Top leaning stroke — a positional marker laid over the cloth radical below. The simplified 币 was rebuilt from 幣, where a longer top 敝 'tattered' once sat. The reform compressed that whole top into a single leaning stroke that signals 'this 巾 is currency, not just cloth'. The mark differentiates 币 from siblings 巾 cloth and 市 market.