As doc-in-the-box billboards go, the minimalist ones that HealthFirst has been pasting up all over town are pretty darn clever. The design is always simple: a solid color background with a few words and the company logo. One, on a brown backdrop, simply asks, "Code Brown?" Another, in front of the Charleston Southern football stadium: "Best Care. Best Price. Amen." All in all, a pretty effective branding strategy.