A light seen from very far, and a mark meaning notable. Both are things picked out of a field.
Old English steorra (a star), from Proto-Germanic *sternō, from a Proto-Indo-European root *ster- (star); marking something as notable borrows the same word for a light picked out of a whole field of them.
A distant point of light, or a mark set beside something to say it stands out. Either way, one thing is being lifted out of a crowd of otherwise similar ones.