[bct]

It's not a lightning bolt, it's the rune ᛋ.

[Animats]

I suspect the "double lightning bolt" is just a glyph to print for end of line, for CR or LF. A tape printer doesn't do anything special for CR or LF, but some of them print something. One of my machines prints "=", and one prints an oversized comma. There's no standard for that.