paper, stationary, document
帋 centers on paper as a material for writing and documents, including stationery and official papers.
帋 is a variant form of 紙, combining 氏 (clan/family) and 巾 (cloth). The exact historical development is uncertain, but it likely represents paper as a material made from cloth fibers and used for family records.
The top 氏 suggests a family or clan, and the bottom 巾 is cloth. Imagine a family's important documents written on cloth-like paper: 帋 is paper for records.
For シ, picture a sheet of paper: sheet -> シ, and the family's documents are written on that sheet.