An excellent heuristic proposed e.g. in the book "Modern Perl" (2015) [1] is to think of $_ as the pronoun it in human language, and @_ as the pronouns they/them.

Edit: a previous HN comment thread on how sigils are derived from practical linguistics: https://news.ycombinator.com/item?id=26659322

1: https://pragprog.com/titles/swperl/modern-perl-fourth-editio...