Growing up I always learned (I think) the “insert missing text” symbol was shaped like the one in the pic, like a caret symbol.

The odd thing is I also remember the caret and inserted word being at the top like in OP’s image, but style guides I can find now show the caret at the bottom and the inserted text at the top.

www.csuchico.edu/…/copy-editing-marks.shtml#%3A~%….

…byui.edu/…/chapter_16_deciphering_elements_of_ha… above (search for caret)

grammarist.com/…/proofreading-editing-marks-symbo…

Wikipedia seems to indicate using a downward facing caret, or a caret with an extra upward arm en.m.wikipedia.org/wiki/Caret_(proofreading)

TIL!

All that to say the formatting of OP’s pic, no matter the direction of the arrow/caret, makes it hard to read. A little “don’t dead open inside” or something.