Are signs stackable in minecraft?

In Steven's video on the EATS water/boat transport system, I distinctly saw him with a stack of signs. However, I cannot stack signs! Is this a mod, or is something wrong with my version?

Solution 1:

Signs can be made to stack, but only through inventory editors such as InvEdit, which will allow you to stack as many as 99, or an infinite amount (255).

In SMP, you can just use the /give command.

Yes, signs stack, but only up to 16.

Solution 2:

Normally signs aren't stackable.

I don't know of any mods that allow you to stack signs, but that doesn't mean one doesn't exist.

Solution 3:

In SMP, if you're an OP (i.e. you can use give) you can give yourself e.g. 64 signs, which when collected will result in one single sign and a stack of 63 signs (for whatever reason).