The problem is, when you break it down all that is is a plain rotated 45 degrees on the z axis, ontop of a stretched cube, with a texture thrown on. If thats your best model, Id have a hard time seeing people bothering to buy any others. If you really want to try and make some money, you might concider just making a sign pack, since you seem to be good at texturing signs. Put together a model of every sign you can think of, street signs, caution signs, no smoking signs, every type of crossing sign, they're all on google, and sell that.