The English verb to be (e.g. "is", "are", etc) doesn't explicitly exist in American Sign Language. Every language has its own "to be" grammatical rules.
For example, the Russian language has the past and future tenses for the "to be" verbs but no "to be" verb in the present tense.
As for American Sign Language, it has its own rules and its own ways of expressing. Its verbs are usually active. Below are some examples of the ASL sentences that substitute the "to be" verbs.
Please note that facial grammar and some grammatical nuances are not included in glossing.
The English "to be" verbs am, is, are are the present tenses. Use some ASL words that tell the present time, such as now and today. Or, sometimes there are no mention of the present-related words which generally tells the present time.
E.g. ix-me fine for I'm fine.
ix-me name fs-jane for my name is jane.
The English sentence ASL isn't English is expressed in ASL as ASL itself not English.
The English "to be" verbs such as was, were are the past tenses. Use the ASL words that tell the past time, such as before, finish, and many other time indicators.
E.g. this morning ix-me suddenly sick laid-back.
yesterday ix-s/he disappointed.
ix-me eat finish
When used appropriately, the ASL verb become is sometimes used.
E.g. ix-me not-want become father for I don't want to be a father.
ix-me not-want become neurotic.
Every language has some words that cannot be translated word by word into another language. Translation is to interpret a concept or meaning in one language that is equivalent to the same concept in another language.
About verbs in sign language.