I suspect all the signs were done by one person. My guess is he tried to make the "handwriting" (spraypaintwriting?) different, but there is a certain larger similarity amongst the characters from the three signs. The white poster suggests to me that this is a clever ad from a print shop, perhaps targeting a rural clientele.

Also, think about this: who would put up a sign saying "need dirt"? That's not a good way to get about getting dirt. It is, however, a good way to get your attention when you're driving down the road.

Da Bing