Let's see. I only know if two ways to cut vinyl. First, which is very uncommon, is to use an exacto knife and freehand the entire sign (vinyl decals are also reffered to as signs).
The more popular method is to use a programmable vinyl cutting machine. You just tell it what you want to cut, and it'll cut it! Most of the time it's easier to just buy vinyl from a custom shop because vinyl is sold by the yard. So unless you plan on cutting lots of the same colored signs, I wouldn't do it.
Let me know if you have anymore questions, I would be glad to answer them! Be sure to check out the 'How to apply vinyl' video my TARC team made on our fundraising site, rocketguts.com Go to 'Instructions.'
Good luck!