I’ve become fascinated with the way that people signal they are selling their vehicles. Virtually everytime I drive somewhere, I see a car that is for sale by owner.

Here are a few styles I’ve seen:

$555-5555 This ambiguous note seems to say "for sale" by using a dollar sign ($) butted up against a phone number. The "for sale" and telephone number are not clear, so maybe that's just the price range.
4-sale 555-555-5555 I like this one. If I saw this car while on a road trip, I'd know it was available and how to contact the seller.
sale 555-555-5555 Not bad, but are they selling their phone number? The note could be more clearly written.
180k $800 5555555 Without more context, I have to interpret this myself. I assume it means the seller wants $800 for their 180,000 mile car and they can be reached at 5555555 (or was that 555555 or 55555555?).
$1000 OBO Here, "OBO" means "or best offer" showing that the seller is negotiable on price. I tend to think most prices are negotiable, particularly when dealing with individuals, however, the "OBO" conveys a great willingness to work with the seller (probably a good thing). Should I just flag down the owner and negotiate while driving?
The personal car advertisement brings up questions of usability and efficiency in generating sales. What's most effective? What information is necessary? I don't know, but here are a few thoughts: * The only constant among the advertisements seems to be a phone number. I think this makes sense, since the buyer needs a way to contact the seller and make the transaction. * In general, I think it's short sighted to put only a 7 digit phone number. Cars, and the people contained within, are mobile. It's not unreasonable to think that you may leave your area code or have others enter yours. * Putting too much information feels counter-productive. * Numbers like price or number of miles are very hard to differentiate from phone number * It is very difficult to assess the vehicle and write down the phone number while driving, so stationary vehicles are probably more effective. I would recommend a clearly written advertisement on the back windshield that states the intention to sell ("for sale") and a contact phone number (10 digits, appropriately separated with dashes). In conjunction, list your car on craigslists, ebay motors, zip zoom auto, and tell your friends verbally and over facebook. And one high-tech idea: put a QR code on a sheet of paper in the window. Boom!