Tire stencils have been around for a while, starting out originally to advertise on racing cars, the trend has been recently picking back up. Some cars just can't seem to do without them, for example: the Shelby Cobra and now RWB Porsches. These serve absolutely no purpose other than promoting the tire brand, nevertheless, they give a very particular style to most cars. 

The most common places to find these stenciled tires is on racecars. It's a "cheap" way to advertise and because the tires spin, it catches people's attention. On some cars it looks really nice, like this GT-R: