I know why tire makers put the dot on the side of the tire .
But why do they put one or two paint rings around the tire on the treads ?

 

It's just part of manufacturing,, they could/can be a number of different things the manufacture uses,, tread identification, warehouse/inventory control, extruder identification, shift/plant identification.
They're just easily seen color coded identification for the manufacturer.

p.s. But you said yours has Two Strips and a Dot?
Oh No! They should not have sold that tire!!

 

article taken from

http://www.tirerack.com/tires/tirete...jsp?techid=173

What Are All Those Lines, Numbers and Letters on a New Tire's Tread?
While tires may appear to be a homogeneous piece of rubber after they are vulcanized during curing in their molds, most tires feature dozens of fabric, metallic and/or rubber components that must be shaped, sized and assembled to exacting specifications. One of the main rubber components is the tread compound, which is typically manufactured by extruding, a process that's essentially an industrial version of squeezing toothpaste out of a tube.

In the case of tires, warm rubber is extruded through a metal die to produce a continuous slab of tread rubber compound that's the appropriate width and thickness for the tire size being manufactured. The slab of tread rubber compound is subsequently cut to the length needed to go exactly one revolution around the tire's circumference.

Tire Tread Identifiers
Multiple stripes and numeric codes are visible on the surface of this new tire's tread.

Since thousands of these flat tread slabs are processed in a tire manufacturing facility every day, the manufacturers often print stripes (often featuring multiple stripes or various colors around the tire's circumference) and/or alphanumeric codes to identify the exact type and size tire for which the tread slab is intended. Because the tread identifying stripes/letters/numbers are printed on the flat tread slab before the tire is assembled and its tread design is molded, these identifiers can be seen on the surface of a new tire's tread blocks, as well as all of the way down to the bottom of the tread grooves.

Since these tread slab stripes/letters/numbers don't have any bearing on the tire's performance and are often specified by each individual tire manufacturing plant, those found on a single tire type and size produced in multiple locations may be different.