Question

what are the rules for sign convention

Answer 1

1)all distances should me measured from pole
2)the direction along the incident ray is treated as positive and opp is taken as negative
3)height measured above principal axis is taken as positive and down the axis is taken as negative

Answer 2

The rules for sign convention are
1) A ray that is initially travelling parellal to the central axis of the mirror reflects back through the focal point.
2) A ray that is initially passing through the focal point of the mirror reflects back to the parellal to the central axis.
It's for spherical mirror
I hope this might help you....