Would You Do This To Market Your Pet Sitting Business?

I hear people tell me often, I don’t have any money to advertise but I need to get my name out there.
Well picture this:
I was driving through Starbucks and I saw a car parked in the parking lot with a sign that said For Sale and the phone number. It was placed smack dad in front of the drive through line. So while you are waiting for your latte, you see this sign staring you in the face.
I thought wouldn’t it be a great guerrilla marketing strategy to put a huge sign in your window like one of those sunshades?
I think this is an off the wall, wonky, eye catching way of advertising because:
So what kinds of things can you do that are a minimal cost but can make you money? For instance, at Starbucks. Let’s just say there is one car every minute in the drive through plus all the people that walk into the actual store. There is probably at least 60 people an hour. That large sign in the windshield would potentially hit all of those people.
Let’s take it a step further and place your business cards on your wiper. So for those of you not wanting to be a mobile billboard all the time with a wrap or magnets, you can do the one time advertisement. Ever think of that?
What do you think? Would you do this in your pet sitting business? Or is it just too guerrilla marketing for you?