This means that you did not add tips to your credit card transactions and you'll need add them to process with the register close.
Go to the credit card transaction settle screen by pressing CC NO-TIP from register close.
Once you are on credit card transaction settle screen, start inputting tips into each transaction by using number pad that comes up when pressing the transaction.
*You could also press Gratuity to adjust the tips
You could finish transaction settle along with inputting tips. See this link for detail: Credit Card (Settle Transaction)
After inputting all the tips into the transactions, you'll see the orange highlight from CC NO-TIP gone.