How to refresh signs?

Hi,
my plugin changes the text in signs with the code

Code:

sign.setLine(3, "blabla");

But the problem is, the players have to rejoin the server to see this changes.
Is there any way to refresh the signs immediately?

Second question: I want to drop a sign, I used the command:

Code:

block.setType(Material.AIR);
world.dropItemNaturally(block.getLocation(), new ItemStack(Material.SIGN));

block is the block where the sign stands, I delete this block (set it air) and drop a new sign at this position.
The sign get dropped, but I cant take it?

 

1.
Use sign.update(true);

2.

Code:

world.dropItemNaturally(block.getLocation(), new ItemStack(Material.SIGN, 1));

I believe you need to set the amount of the itemstack too..could be it was set at 0 items.

 

Both works, thanks a lot!
sign.update() works too