Take a large box and cut a hole you can pull up around your body. Then paint the outside of the box yellow with big black letters spelling TAXI add straps to the box like a seat belt and a licence plate.
You can also add "how's my driving" or "save the whales" bumper sticker, you can even put flash lights in the front like your headlights.
You will of course need a steering wheel and cool hat. A name tag is fun too
Thanks to anonymous submitter for this funny idea!