According to Old Currency Values, a red seal five dollar bill from 1928 is worth $7 in circulated condition. These bills can be worth about double in uncirculated, perfect condition.
The 1928 red seal five dollar bill was part of a series of bills created in three different years. The other years that red seal five dollar bills were issued were 1953 and 1963. These bills can not only be identified by their red seal, but can also be identified by the red serial numbers on the bills.
While the bill may not be worth much more than face value, they are common to come across. Because of their availability, they will have a lower price, but collectors will be able to collect more of them and turn a larger value that is dependent on the quantity of the bills.