not too secretive. And there are tons of ways to do signs on trucks and tons of folks who print banners. but I am finding I need to give some value to my consulting clients that I don't give away for free.
I will tell you though, having the photo on the boxvans at that size, gets us work. I have an older enclosed trailer rig that has no photo, but has nice 3m vinyl graphics and phone numer,but no callers mention it anymore. but they mention the picture of the houses.