What Happened to the Blue Seal?

Back in the 1870's, the years that Morgan Dollars were first introduced and struck, silver certificates were also introduced and printed. They had a blue seal to show that they were silver certificates rather than gold certificates or United States notes. They basically said that for every printed silver dollar, there was a physical silver dollar in the treasury. Of course, when silver coinage was mostly discontinued in 1964 these were not accepted as much and eventually in 1967 you could not use them in exchange for silver. This is one I bought recently and had framed. It is worth about $4.00.

(NOTE: The picture quality makes the bill look worse than it actually is.)