I can't remember terribly much about the book. I think it was fairly large for a child.
The main character is a teenage girl. She is part of a family/clan who all have very specific superpowers. They range in intensity and specificity, but hers was on the low end. Tattoos could speak to her, and could tell her the inner thoughts of the person to whom they were attached. This worked even with temporary tattoos and ink drawn on skin.
I remember a minor subplot of her dealing with her attraction to a boy that gets drawn into whatever the major conflict is, but has no powers (wrong place/wrong time deal).
The major source of transportation is a yellow ex-school bus that is a main feature of the family. It also appears on the cover.