You can find "Show +/- signs for transactions" in MoneyWiz Settings (gear icon in the menu) > List of Transactions. When it's enabled, transaction amounts will appear in black or white font color (depending on whether MoneyWiz was set to use Light or Dark theme). You'll be able to distinguish expenses and incomes using the - and + signs that appear next to each transaction amount.

If you disable this setting, the transaction signs will be hidden but instead you'll see transaction amounts in red for expenses and green for incomes.