A United States $1 bill with a blue seal on it is called a silver certificate and ranges in value from face value for common varieties in normal condition up to $150 for a particular type of 1928 bill in excellent condition, as of 2014. The value of silver certificates depends upon rarity and condition. In the same series of currency, uncirculated bills are worth more than used ones.
The most common silver certificates are from 1935 and 1957. As of 2014, these notes are worth $1.25 to $1.50 in circulated condition and $2 to $5 in perfect, uncirculated condition. Exceptions include star notes, Hawaii notes and North Africa notes. Blue seal notes from 1934 are also common and are valued at less than $12. The most common large-sized U.S. currency is the 1923 silver certificate worth around $20.
Silver certificates were issued by the U.S. Bureau of Engraving and Printing from 1878 to 1968. The notes could be exchanged for the face value in silver--for instance, a $1 silver certificate was worth $1 in pure silver. This exchange policy ended in 1968 and the bills were no longer printed. Silver certificates are still worth face value as legal tender in the United States.