What does negative sign in magnifying power of telescope denotes

@ altaf , the negative signs means the image will be inverted , as in magnification we are taking the raio of the height / distance of image / object ,, 
so, if in the case of telescope , the image will  be inverted , then u have to put the -ve sign in the equation . 
otherwise , if the image is erect , then no need to put -ve sign. 
HOPE IT CLEARS YOUR DOUBT 
ALL THE BEST ..