Please tell me the proofreading mark for "Write out in full."
Proofreading marks are very specific and well defined. There are twenty-six well known proofreading marks. The mark indicating that something in a text needs to be written out in full is identified as the "Spell out an abbreviation or a number" mark. It may be confused with the "Reconsider word choice" mark or with the "Check the spelling of a word" mark. You can see that though these may seem similar, each has a very specific and well defined function.
To make the "Spell out an abbreviation or a number" mark, or symbol, which may also sometimes be called the "Write out in full" mark, or symbol, you simply draw a distinct and neat oval around the abbreviation or number in question that needs to be written out. The oval will be widest from side to side regardless of the size of the abbreviation or number.
This symbol may be confusing because it is identical to the "Abbreviate a word" symbol: both symbols are an oval. What differentiates the one from the other is that the one oval encloses an abbreviation or number that must be written out in full, while the other oval encloses a fully written word (or number) that must be abbreviated (or written as a numeral).
I'm not sure if this is the exact answer you need, but if you're talking about telling the writer to use a whole word instead of an abbreviation (i.e., using "ounces" instead of "oz"), you would circle the abbreviation and next to it write an "sp" with a circle around it. This stands for "spell it out."