In the Finale episode of The Office, we learn that one reason Kevin was fired, was for using his made-up number "kelevin" to correct accounting errors. His replacement is seen asking Oscar about this "strange symbol." Do we have any way of knowing what this symbol looks like?
So the keleven, as you say, was used by Kevin to balance the books:
Oscar: [on the phone] Years ago, the senator promised a left turn lane by the Arby’s. So I wanna know where in the name of horsey sauce is it? Well, yeah, you…hold on.
Dakota: Hi. I keep seeing this symbol in the accounts from last year. It’s..it’s all over the place. I don’t know what it means.
Oscar: That’s the reason Kevin got fired. It’s his magic number. He used to use it to balance his accounts. He used to call it a Keleven. He told Dwight, [imitating Kevin] “A mistake plus Keleven gets you home by seven.” He was home by 4:45 that day.
Aside from these words and despite extensive googling, there is absolutely no reference anywhere to what the symbol might actually look like. I even went through a combination of different searches on google images and instagram, but came up empty handed.
Therefore, I'm going to say no, we have no way of knowing what the symbol looks like as the producers of the show have never attempted to release it (and have likely never even created it).