Thank you for this question. I have an answer! The two column headings are mnemonics for students to remember how to count oxidation numbers.

R means Reduction; G means gain (the species is gaining electrons) …so the oxidation number goes to the left on the number line (becomes more negative) or goes down (down arrow).

O means Oxidation; L means losing (the species is losing electrons) … so the oxidation number goes to the right on the number line (becomes more positive) or goes up (up arrow).

The arrows have no chemical meaning and are just representative of a direction of how the numbers increase or decrease.

With that in mind, I suggest using Nemeth arrows here, preceded and followed by a space. See attached file. Because these are column headings, I am including the seven rows in the transcription.

FYI: Another mnemonic that is used is OIL RIG (oxidation is loss, reduction is gain) for students to remember how the electrons are transferred.