Coins that share a symbol
The warning
Symbols are not unique: more than one project can call itself, say, SOL or BTC. When your list holds two different coins with the same symbol and the title style for the current layout is Symbol only, the Title area controls show a note: ⚠ SOL is shared by two of your coins, with Symbol only they'll look identical. Add Icon to tell them apart. With more than one clash it reads are each shared by.
What to do
Choose a title style that includes the icon or the name for that layout, and the two coins are told apart on the glass. The note tracks the saved coin list, so it appears once the second coin is saved and disappears when the style changes. In Four per screen, where each row has room for one field, choose Icon.
Symbol only, the style the warning is about, next to Icon + Symbol, which tells the two coins apart:



The same coin twice is a different case: see Can I show the same coin twice?.