A note about positive vs. negative stencils: When you cut out a stencil you have two stencils - A Positive stencil (what you cut out) and a Negative stencil (the hole left where you cut the positive out). For this stencil project I will be using a Positive stencil because I want the "background" of my tshirt to be bleached and the design itself to remain the original color of the T-shirt. Just make sure when you're designing for your stencil that you know which parts you want masked and which parts you want to bleach! You can read more about positive and negative stencils here.
Why vinyl? I'm using vinyl because I wanted to get sharp lines on an image that included some fine lines and I wanted to have text without using "stencil lettering" (where all the parts of the letter are connected). I also wanted to make multiple tshirts and vinyl seemed the best means of repeating the image over and over.
What's the story behind the stencil image? A conversation at a party turned to the discussion of a news article about bears in Russia who are making a habit of huffing empty jet fuel barrels (poor bears!). This conversation generated the phrase "Russian Kerosene Bears", which in turn lead to the creation of a logo for a fictitious product/cover band/candy/anti-theft device/biker gang/etc. T-Shirts featuring said logo seemed the obvious next step.