I think you are confusing the Federal Reserve district letter - the large letter inside the circular seal - with the series letter. The series letter, if there is one, appears next to the date. The highest series letter on a $1 bill was H, on the last silver certificates from the 1935 series.
In any case, if you have a green-seal Federal Reserve note, none of these have any extra value if they've been circulated. Uncirculated $1 bills from 1963-69 might sell for as much as $2, that's all. Everything else is face value even if it's uncirculated.
No US $20 bill carries a "G" series letter. You may be looking at the Federal Reserve District letter. The series letter, if any, on US bills is next to the date. Regardless, a date is needed in order to estimate a value. Please determine the bill's date and see the question "What is the value of a [date] US 20 dollar bill?" for more information.
A 1990-series $20 bill is too new to have any added value. Some of them are still in circulation.
A date is needed. Please see the question "What is the value of a (date) US 20 dollar bill?" for more information.
You didn't provide a specific date but 1969 is the only series in the last 50 years to have a "B" letter. Please see the question "What is the value of a 1969 B US 20 dollar bill?" for more information.
None of them. 1950-series $10 bills remain common among collectors. There's more information at the question "What is the value of a 1950 US 10 dollar bill?".
Sorry, there is no such bill.
I would like to the current value of excellent condition of 1862 US series 268 1 dollar bill.
C is the highest series letter on a 1953 US $2 bill. The series letter, if any, is next to the date. Please see the question "What is the value of a 1953 US 2 dollar bill" for more information.
Its worth no more than its face value. 2$
Check the date or rather series again. US dollar bills were not made in 1960.
Check the date or rather series again. US dollar bills were not made in 2010.
Check the date or rather series again. US dollar bills were not made in 1920.
No US $20 bill carries a "G" series letter. You may be looking at the Federal Reserve District letter. The series letter, if any, on US bills is next to the date. Regardless, a date is needed in order to estimate a value. Please determine the bill's date and see the question "What is the value of a [date] US 20 dollar bill?" for more information.
There are no U.S. notes with the series date of 1921
nothing
The US printed both $2 and $5 bills with red seals in the 1963 series. Please see the questions "What is the value of a 1963 US 2 dollar bill?" and "What is the value of a 1963 US 5 dollar bill?" for more information.
Check that bill again. There are no $2 bills with a series year of 1979.