T.K.
Since the nature of your company is printing and graphic art, I wouldn't do a tag line. Car signs are hard to read. Especially if they are too busy. I would create a visual impact that gets the message across that you are trying to send. I assume your message is - I do quality printing and am good at graphic design. So create a graphic design and a put your name, phone number, and underneath it list a few of your services in a very clear, easy to read way. It needs to be something you can easily read from 10 feet away. Honestly, when I see a clever tagline, I feel like it's an amatuerish company. It doesn't say quality to me. If I were you, I'd focus more on showing your talent as a printer, and graphic artist.