"用记号标出" can be translated into English as "mark with a symbol" or "mark out with a sign", depending on the specific context and the type of symbol or sign being used.
If you're referring to marking something with a general symbol (like a star, checkmark, or other identifying mark), "mark with a symbol" is a suitable expression.
If you're emphasizing the action of physically or digitally outlining or highlighting something with a specific sign or marker, "mark out with a sign" could be used, though "mark with a symbol" is often more versatile and commonly used.
In many cases, a simpler and more direct translation like "mark" (when the context makes it clear what is being marked and how) or "highlight" (if the marking is for emphasis or to draw attention) might also suffice. However, for the specific phrase "用记号标出," "mark with a symbol" provides a clear and accurate translation.