On your attendance screen for the day, you will notice on the right-hand side that the family balance is displayed.
Amounts in green mean that there is a $0.00 balance or the account is in credit (and it will show the amount), such as: 
Amounts shown in red are monies owing. There are instances where the payment amounts are accompanied by symbols, such as:
The 30-45 means that there has been 30 to 45 days since a payment was last received on this family's account.
The +45 means that there has been more than 45 days since a payment was last received on this family's account.
They are there as a flag for you to see who you may need to chase payment from when they attend their lesson that day.
NOTE: If you run lessons by term and have just done a billing run, these flags will show as it generally will have been over the 30-45 days since you last received payment.