Signs are one of my favorite blocks in minecraft and I have found a myriad of uses for them. In this thread I hope to show people a few of the things I have found. This post will be undergoing quite a bit of revision as I remember tricks with signs and eventually add screenshots demonstrating what I mean.
Signs are an amazing thing because of a few simple properties of theirs.
1. they can be placed on any solid block
2. They stop water and lava and do not burn (perhaps the most important aspect)
3. In accordance with number 1, signs can be placed on signs allowing many visual tricks
4. signs stop arrows that hit them, but not creatures
The easiest and perhaps most useful sign trick makes use of property 4. Signs can be used to make dog doors. By opening a hole in the side of your house and placing a sign it it, you create a 1x1 opening that mobs can pass through, but which arrows can not be shot through, both because of the angle that the skeletons would have to shoot at and because any arrows that hit the sign will stop. any 1x1 mob can enter the hole but as only wolves pigs and chickens are 1x1 or smaller it is safe for normal minecraft. (mo'creatures users beware of wild wolves)
screenshot coming eventually.
The second most useful thing signs can do (and IMO the most AWESOME) is create hall lights (which sounds really boring) look at the screenshot.
If you orient this correctly you can not get burned, even if you walk as close to the lava as possible. (Follows the NSEW rules, though if I understand correctly that is getting fixed in 1.6 making this perfectly safe.)
You can also take this farther and make monuments of floating lava (some people will remember this from the LoH server.
To be extra sign loving, build the entire contraption out of signs
Much more coming once I have the time to write it up and get screenshots (most are visual tricks best explained with screenshots), this is the tip of an iceberg.
