This post maybe technical in nature.
On a rifle/shotgun, there is a thing with lenses that has two lines crossing at a right angle and you look through it to aim at the target. Dictionaries suggest "sight" and "sights". Do native speakers call it "sight" or "sights"?
I think that the plural form is more common.
Context is always important; labelling is rarely important.
a gun may have an optical/ laser / telescopic .... sight.
A rifle comes equipped with "sights" that is to say a rear sight and a front/fore sight. An additional "sight" can be added for increased accuracy. For hunting this would most commonly be a telescopic sight.
You are describing the "cross hairs" on a "scope."