What is the value of a 1953 US 5 dollar bill with a red seal?

The red seal indicates the bill is a United States Note, a form of currency printed from 1862 to about 1971. Retail values as of 02/2011 are approximately:

No letter next to the date: $5-$12 in circulated condition, $30 uncirculated.

"A": $5-$9; $12

"B": $5-$8; $12

"C": $5-$9; $30
Twelve dollars
In circulated condition, 1953 red-ink $5 bills are worth anywhere from face value to $8 depending on the amount of wear.

If the bill is uncirculated, it might retail for about $12 unless there is a small letter C next to the date. That particular series goes for about $30 uncirculated.

The use of red ink indicates that your bill is a United States Note rather than a Federal Reserve Note. U.S. Notes were a kind of parallel currency that circulated alongside FRN's until the 1960s when they were discontinued to reduce the overhead of printing multiple types of bills.