There's not much to go on

[Smythe, Boyd T {FLNA}]

> Anyway, I thought Jo had stated that it wasn't a rune? Or is that my
imagination?

Another interesting quote (thanks to QQQ):

Bolger, Kaitlin and J.T. Sprague. "J.K. Rowling answers a few kid
questions," Houston Chronicle (conference call), March 20, 2001.
Q: What is the meaning behind Harry's lightning bolt scar?

A: There are some things I can tell you about it and some things I can't. I
wanted him to be physically marked by what he has been through. It was an
outward expression of what he has been through inside.

I gave him a scar and in a prominent place so other people would recognize
him. It is almost like being the chosen one, or the cursed one, in a sense.
Someone tried to kill him; that's how he got it.

I chose the lightning bolt because it was the most plausible shape for a
distinctive scar. As you know, the scar has certain powers, and it gives
Harry warnings. I can't say more than that, but there is more to say.

--boyd