It could not be a Series O - 1950 series letters only went up to E. The series letter is next to the date; my guess is you're looking at part of the serial number.
Despite its age, most 50's of that vintage are not worth much more than face value. Nice specimens might retail for as much as $70. The only exception is a 1950-E which retails in the $75.-$150. range.
The lack of a motto is NOT an error. It wasn't added to bills until the late 1950s and early 1960s, mostly in response to the anti-communist hysteria of the time as a way of showing the U.S. to be different from the "godless communists".
The motto In God We Trust was not added to bills until the late 1950s and early 1960s so that's not a misprint. However, you do have a nice find - this series retails at between $75 and $200 if circulated, and for up to $500 if uncirculated and unfolded.
What is a 1950 one hundred dollar bill without "In God We Trust" worth?
You need to post a new question with the bill's date. It wasn't added to paper money until the late 1950s and early 1960s so your bill is NOT an error, it's just older than those dates.
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Without knowing its date and series letter it's not possible to give a value. The motto In God We Trust wasn't added to bills until the late 1950s and early 1960s so if the bill is older, it's perfectly normal if the motto's not there.
The motto " In God We Trust " was added to dollar coins in 1866. There was no mintage of 1871 dollars without the motto.
No, 1950 series E one hundred dollar bills do not have the phrase "In God We Trust" printed on them. The motto "In God We Trust" first appeared on U.S. currency in 1957.
No, it has In God WE Trust. Earlier coins in the series have the phrase engraved around the edge, while later coins have it on the front.
The motto In God We Trust didn't appear on US $10 bills until 1963 so it's not a mistake on a 1934-series bill. There's more information at the Related Question.
Between $6 and $30, depending on the condition. Not having the In God We Trust legend is normal for this series. It first appeared on $5 bills with series 1963 US Notes.
All 1935-E Silver Certificates were printed without the words "IN GOD WE TRUST" ... this was not added until Series 1935-G. In circulated condition, it's worth about $2.00 A nice crisp uncirculated one is worth about $5.00
As you can see from the backs of modern paper money and the fronts of all US coins the motto is In God WE Trust. It was added to $1 bills starting with the 1935-G series so a 1935-E bill without it is normal and not an error. Please see the Related Question for more information.