I've seen everything from balloons to poster board signs to achieve the same goal and not only do they look tacky but they can be easily missed. Even the smaller DIY wooden signs look nice, but don't stand out. I love the idea of using an entire pallet to provide information for your guests, be it where to turn, where to pee, a special quote or what's on the menu.
What I like about these signs is they don't require removing each plank, using a Kreg Jig to attach the planks tightly together, or even a saw to smooth out the edges (similar to the sign in the top image). That's all fine and dandy and can produce a beautiful sign like the one in this Pinterest post, but I'd probably saw off a finger or two so not for moi. I say keep it simple and use the pallet as-is, gaps and all. and stencil (or paint) away! It will be memorable nonetheless.