On your tax bill, it clearly states which type of taxes you owe: Secured, Supplemental or Unsecured. If you don't have your bill or your bill does not say which type it is, you can identify what type of taxes you owe by checking the upper left corner of your bill.
Secured Tax bills have a tracer number with the first digit between 0 and 4.
Supplemental Tax bills have a tracer number with the first digit between 5 and 9.
Unsecured Tax bills have a 19 digit assessee number separated by dashes.
For further information about the differences between Current Year Secured, Supplemental and Unsecured payments, read the Property Tax FAQ's.