I think people do notice signs and billboards if they are in a visible location... even if they don't jump out at us, we see them.
If they are of any interest to us, we notice them.
Somebody driving down the road who has no interest in a vehicle wrap will see this billboard once or twice, maybe more if they like to look around, but will take no real notice of it.
But, someone driving down the road who has been thinking about getting a vehicle wrap, or want to know more about them, will take more notice in this sign.
Just because a billboard can make me laugh or has something that "makes" me look at it doesn't mean I'm going to give 2 squats about the product being sold unless I have an interest in it to begin with.
I, personally, think that many billboards are out of control with attention grabbing gimmicks and are beginning to look spammy and are losing the feel of a quality product or service.
It's like when I'm walking through the mall, looking around at the different stores and some sales person from a kiosk jumps out in front of me with a sales pitch shoving his product in my face giving me every reason why I need it.
I understand the need for things to be of visual interest, or at least pleasing to the eye, but I don't think they need to scream at every person driving by day after day after day.....
Which is what the majority of traffic driving by your billboard will be, daily commuters who drive past that spot and past your billboard at least 5 times a week on their way to or from where ever they're going.
There's a billboard just outside of madison, wi that has a plane or something on it that is highlighted with a spot-light and makes it look like it's coming right at you. I actually swerved the first time I saw it because I thought I was about to be hit. To me, that's just not cool.