It looks like Taco Bell is promoting its new website and Ta.co domain name on Twitter. If you have a look at Taco Bell’s Twitter page, you can see the company has a Ta.co graphic background, and the avatar also has a Ta.co logo. The promoted url is also Ta.co.
When you visit Ta.co, you are redirected to Taco Bell’s website, which can be found on TacoBell.com. I think this is a simple marketing tactic to capitalize on the short ta.co url. Here’s what the company says about Ta.co on its website: