Symbols used when marking up copy are called:

The term that refers to symbols used when marking up copy is proofreader's marks. These marks are standardized symbols that indicate changes, corrections, or adjustments needed in the text. They are crucial in the editing and proofreading process, ensuring clarity and consistency in the final document.

Proofreader's marks help delineate specific instructions, such as where to add or remove text, correct spelling mistakes, or adjust punctuation. The use of these marks allows editors and proofreaders to communicate effectively with writers or typesetters without altering the original text directly, facilitating a clear understanding of the modifications needed.

While other terms such as editorial marks or correction symbols might generally refer to similar functions, proofreader's marks denote a specific set of conventions recognized in the publishing and editing industry. This distinguishes them from other marking systems that might be used for different purposes, like annotations which are typically more subjective and personal in nature.