Final answer:
In SPL (Streaming Programming Language), a comment is signified using the syntax of //, similar to many other programming languages.
Step-by-step explanation:
In SPL (Streaming Programming Language), a comment is signified using the syntax of //, similar to many other programming languages. This syntax allows you to write comments that are ignored by the compiler or interpreter and are only meant for human readers. For example:
// This is a comment
// This is another comment
The other syntaxes mentioned in the question, such as "comment", ::comment::, `comment`, and (comment), do not signify a comment in SPL.