I don't think a cert is the answer to your problem. Because then a large % of people would study and pay just to get the cert and continue to write crap code anyway. Meanwhile a certain % of other people who can't/don't want to get the cert will continue writing beautiful code.

If you're concerned about filtering out people who write ugly, hard-to-maintain code, how about more portfolio-based hiring? Want a programming job? Show me an impressive piece of source code you've written, and explain what design patterns you employed and how it is an elegant and maintainable solution to the problem it was written to solve.