Is a plus sign against halakhah, or offensive?

Philologos writes that

the arithmetic textbooks of the Israeli ministry of education have, under Orthodox pressure, lopped off the top of the plus sign.

I assume this is true, although its unclear if this is only for certain textbooks in certain schools in Israel.

Wow. It's a good thing we use Aramaic and not Hebrew script, because the ancient letter tav was in fact more or less the cruci-plus sign: +.