what is the symbol of a plus sign over a minus sign ±

$$7\pm8=7+8\;\;OR \;\;7-8\\\\
$So there are two answers, 15 and -1 are both correct answers, you need BOTH of them to make a whole answer! $$$

If you saying negative sign and positive sign, it'll be negative sign, since they have no equal sign. If it was both nagative sign, it's going to be positive sign, therefore they had same sign.

± is called the plus-minus sign. Hope that helps.