The Voree Plates seem to be definitely written in an unknown alphabet.

Savangin is a pre-historical natural cave with an inscription written unknown or unsolved alphabet in Yusufeli town of Artvin, Turkey.

Not only strangely shaped but in an unknown alphabet, unknown that is, at least to me.

The globe hung before her, the lights mysterious as words written in an unknown alphabet.

Their constellations looked to Drawlight like gigantic, glittering letters letters in an unknown alphabet.

Bart thinks the characters represent a previously unknown Tholian alphabet that relies on tones.

One of them, a heavy tome with an iron clasp, was in another unknown alphabet - this one of a very different cast, and resembling Sanskrit more than anything else.

The trees which ringed the grassy pavilion on the hospital's north side were half denuded now, and the black branches were limned against the gray sky like giant letters in an unknown alphabet.

A third suspicious letter was in an unknown tongue and even an unknown alphabet.

In addition, the Book of Sand is written in an unknown alphabet and its content is not obviously random.