Up close you can see at least three 'hairs' of rubber from this picture from the side of my tyre:
Why do they exist? I've heard they are just a bi-product of the manufacturing process.
They serve no purpose on the finished tire, but they are a consequence of a very important detail of the fabrication process.
While rubber is being injected in the mold, there are risk of air bubbles forming between the rubber and the mold, which can prevent the rubber from getting in all the intricate patterns of the mold, thus producing malformed tire.
That's why the mold has vent holes that allow air to get out. A little rubber gets squeezed into these holes and that is what causes these "hair".
These hairs have no useful purpose as long as riding concerns, so they can be removed with no consequences.
Those are "sprues" -- bits of rubber that went into the vent holes in the tire mold. They serve no purpose.