Please check your bill again. There are no 1968-date $1 bills. "Barr notes" are dated 1963.
There's more information the at question "What is the value of a US 1 dollar bill signed by Secretary Joseph Barr?"
Internet frenzies to the contrary, "Barr dollars" are neither rare nor valuable.Please see "What is the value of a US 1 dollar bill signed by Joseph Barr?" for more information.
I asked you first
Joseph W. Barr died on 1996-02-23.
Joseph W. Barr was born on 1918-01-17.
Joseph M. Barr died on 1982-08-26.
Joseph M. Barr was born on 1906-05-28.
Clarence Barr died in June 1968.
Keith Barr was born on 1968-01-26.
Al Barr was born on 1968-09-12.
"Barr notes" have an undeserved reputation for rarity because Joseph Barr served as Treasury Secretary for only about a month at the end of the Johnson administration. However, notes bearing his signature were printed in large quantities before new ones were prepared for Nixon's administration. As a result Barr notes are common among collectors. As of 02/2009 U.S. Currency Auctions lists a fair market value of an uncirculated Barr note at only $2.00. Many sellers on eBay are under the mistaken impression that these bills are rare - or are trying to play off others' lack of knowledge - and are attempting to charge highly inflated prices.
Please check your bill again. The last US $100 silver certificates were dated 1891, and the last silver certificates of any denomination were dated 1957. Joseph Barr was Treasury Secretary at the end of the Lyndon Johnson Administration so his signature could not be on a bill for either of those dates.
An uncirculated (no wear or folds at all) bill with his signature can go on ebay to a collector for up to $5.