Imagine a **market** stall. The top `亠` is the roof of the stall, and the bottom `ム` looks like a person's legs walking around the market, looking for things to buy.
'Shi' — sounds like 'city'. Think of a **city** full of **shi**ny buildings.
'Ichi' — sounds like 'itchy'. You might get an **itchy** feeling when walking through a crowded **market**.