ONE in sign language
One evokes a dot in 3-dimensional graphic, the first, the beginning, a single, ...
ASL signs for 'one'
"What is the numeral sign for 'one' in American Sign Language?" And how to use two versions of the palm orientation.
Meaning: The lowest cardinal number; half of two; the numeral symbol of 1.
Pronunciation (sign description): Dominant index finger or forefinger is upright while the rest of the fingers and thumb are closed. For a cardinal number, the orientation of palm faces the signer. This handshape is glossed as "1".
Usage examples: "one thing", "have one book", "only one".
Unlike the cardinal numbers between one and five, the palm orientation is outward for age, time, phone number, address, and a few others.
Usage examples in ASL glossed as "AGE+ONE" ("one year old" in English), TIME+ONE ("one o'clock" or other variations).
The "1" handshape seems to be prominent in American Sign Language of the Deaf people. It's found in such as pronouns, some determiners, and gestural pointing.
Nothing relating to the number 'one', the "1" handshape is one of few unmarked handshapes. As ASL has over 50 handshapes, only about 7 of them are unmarked, which mean, in the shortest explanation, "natural".
The "1" handshape is one of few first handshapes emerging in language acquisition (particularly phonological acquisition) under age 2 or 24 months.
English in spoken version has about 40-44 phonemes, whereas ASL has 50+ handshapes. During the first 24 months of language acquisition from birth, a few phonemes no more than 10, such as "n", "p", "b", and few others emerge in language during the first 2 years. In ASL, similarly, no more than 10 handshape primes, only a few handshapes emerge during the first 24 months. After than, more phonemes and primes respectively increase up to 8 years.
Signed and spoken languages, even though contrast in modalities (visual-spatial vs aural-vocal) and completely different languages, both parallel in how brain works in language acquisition, language development milestones, and such. Baby sign language is harmful cultural appropriation with common misconceptions about the nature of language; "baby sign language" is no more illusion than "baby speech language".
"One" around the world
As signed languages are not a universal language, they all are incomprehensible to one another. Although, very few ones are in common, such as the number one.
In Australian Sign Language also known as Auslan, the numeral sign for 'one' is the same as ASL, but for "six", thumb is involved as the re-start of counting toward ten.
In Japanese Sign Language and many other signed languages, the number "one" uses the "1" handshape (with a different rule for palm orientation found in ASL).
In North America, the ASL word 'one' uses a forefinger, while most signed languages in Europe, the thumb is a common handshape for the word "one", as found in French Sign Language (LSF), German Sign Language, Polish Sign Language (PSL), and others.
In contrast to other signed languages in Europe, the handshape for number one in BSL (British Sign Language) is the same as ASL. Though, the manual alphabets in ASL and BSL are completely different.
A culturally competent person can easily distinguish this signed word from the "thumb-up" gesture.