They are called "mold sprues"...and about a dozen other names.
They serve as gas vent paths to insure full mold filling. As liquid polymers (rubber) are forced under injection pressure or mold vulcanization, air and gases produced by the molding process must exit the mold. It does so thru spues and vents located around the circumference of the mold cavity.
The molding machine operator, upon extracting the finish molded tire from the mold cavity, can quickly inspect the product for full mold fill by checking for the presence of the sprue nubs...AKA as tits, whiskers, hairs, etc.
In other casting or molding industries they may be termed mold risers.