This depends on the type system and the language.

Many languages have a type for this, for example never in TypeScript, Nothing in Scala and Kotlin, and Haskell also has one, although the name escapes me at the moment (bottom?).

C has a _Noreturn function specifier keyword.

In languages that support annotations (e.g. Java, C#), you could create a custom annotation that communicates your intent. Some IDE vendors or static analyzers might already have invented one for you.

Otherwise, documentation is the best thing you can do.

A type such as this is often a bottom type, meaning a type that is a subtype of every other type, and it is a type that can never have any instance. (This is called an "uninhabited" type.) Since it cannot have any instances, declaring the return type of a function as this type clearly communicates that the function never returns, since there is nothing it could return.

This depends on the type system and the language.

Many languages have a type for this, for example never in TypeScript, Nothing in Scala and Kotlin, or Void in Haskell.

C has a _Noreturn function specifier keyword.

In languages that support annotations (e.g. Java, C#), you could create a custom annotation that communicates your intent. Some IDE vendors or static analyzers might already have invented one for you.

Otherwise, documentation is the best thing you can do.

A type such as this is often a bottom type, meaning a type that is a subtype of every other type, and it is a type that can never have any instance. (This is called an "uninhabited" type.) Since it cannot have any instances, declaring the return type of a function as this type clearly communicates that the function never returns, since there is nothing it could return.