I don't advertise anything on my vehicles other than base stickers.
I did train everyone in my family to put their hands on their heads if I ever get pulled over. I expect that my CCW permit will show up, they will expect that I am armed, and seeing a minivan with wife and 3 young children with hands on their heads would have to seem pretty amusing to a police officer. And if they don't think it's funny, then (*&^ them.
I have plenty of Glock and Sig and XD stickers, and I don't put them on my cars either. I might as well stick them on my my hard cases, because it is pretty obvious what is in there anyway.
A long time ago, I thought it was cool to have a CCW permit. I've grown up. I'm sure that in hindsight, anyone would have to admit advertising something that is supposed to be concealed is kinda silly.