A maintenance signal flag adapted for use with a shopping cart, the maintenance signal flag comprising a flag member and signal panel hingedly connected to a mounting assembly. The mounting assembly secures the maintenance signal flag to the shopping cart, and flag member pivots between raised and lowered positions to raise the signal panel above the shopping cart. The signal panel displays a maintenance message when raised, indicating the shopping cart is faulty. A user, upon discovering a defect, raises the flag member to create a visual alert which warns other users to avoid the faulty shopping cart and notifies maintenance personnel to service the shopping cart. The maintenance message identifies the specific defect to facilitate efficient inspection. The maintenance signal flag may be retrofitted to existing shopping carts and does not interfere with the ability of the shopping cart to be stacked with other shopping carts.