The Street of Smiles, Hué (Photo)

Street in Hué with lots of smile signage

I'm guessing dentists, but I'm not sure.

[2015 update: Google Translate says "phong rang" = "style roast" (it auto-detected Vietnamese), but if you actually add the accents, "phòng răng" = "dental." More narrowly, "phòng" = "room," "răng" = "tooth."]