Where r her tatoos???

Ok, you are definitely right about the confusion over her mga tattoo because of her role on The OC and other movie roles, BUT she does have at least one tattoo of her own. If you pay close attention to this litrato (link) (and yes I have paid very close attention to it!), you can see a tattoo on her upper butt!
In an interview with GQ she says she got it when she was 13 years old. You can't see it very well, but it looks like a dragon or a snake type thing or something like that (I dunno just a guess). People around the internet say that its the name of her boyfriend at the time, but it doesn't look like a name to me. I guess it might be a symbol of his name, or she could have had it altered later on.
I'm pretty sure that is the only tattoo she has, unless she has some really well hidden ones, which is very possible.