How do I add a text overlay to a masonry gallery?

Hi,

Suppose I want to add a text overlay to the masonry gallery that’s on the home page. I want to put a big mission statement there. How would I go about doing that?

http://awesomescreenshot.com/0033m55ta8

So suppose the map in the background was a 4×3 masonry collage. What I’d like to do is add text over that just like in this screenshot. Centered and I’d like to be able to control the size, line-height, etc.

Thanks,
Gabe