https://en.wikipedia.org/wiki/Fig_sign

giving someone the finger¿ средний палец¿

Но грубее

И смысл другой.

Согласна.
Letter T¿
https://www.babysignlanguage.com/dictionary/t/letter_t/

"The letter "T" in the American manual alphabet is very similar to this gesture."
это не означает, что у этого жеста может быть такой же смысл.

Можно найти и такое:
“Dulya”, also known as the “fig sign” or “shysh”, is very much exercised in Russian dominated or influenced territories, including Turkey, Indonesia, China, and other countries. It is an extremely offensive sign comparable to the middle finger in the US and other

Я не согласен, что это "extremely offensive sign comparable to the middle finger"

В некоторых объяснениях можно встретить "sign/gesture of denial".

https://brightside.me/wonder-places/15-hand-gestures-that-have-different-meanings-overseas-769110/

America: The thumb between the index and middle fingers represents the nose stolen from a kid’s face in the “I’ve Got Your Nose” game.
Turkey: An obscene gesture similar to the middle finger, and is also used to show disagreement or to deny a request.
Brazil: A good luck charm to ward off the evil eye and jealousy.
Indonesia: An offensive gesture.
American Sign Language (ASL): The sign for the letter T.

https://www.google.com/search?source=univ&tbm=isch&q=sign/gesture+of+denial&client=firefox-b-d&sa=X&ved=2ahUKEwjF_ciHlrzqAhWC-qQKHQf9DawQ7Al6BAgKEDE&biw=1079&bih=705

https://www.iconfinder.com/icons/2753724/denial_disagree_gesture_palm_reject_icon (?)