--- a/net/minecraft/world/level/block/entity/TileEntitySign.java
+++ b/net/minecraft/world/level/block/entity/TileEntitySign.java
@@ -31,7 +31,17 @@
 import net.minecraft.world.phys.Vec3D;
 import org.slf4j.Logger;
 
-public class TileEntitySign extends TileEntity {
+// CraftBukkit start
+import net.minecraft.EnumChatFormat;
+import net.minecraft.nbt.NBTBase;
+import net.minecraft.server.level.EntityPlayer;
+import org.bukkit.craftbukkit.block.CraftBlock;
+import org.bukkit.craftbukkit.util.CraftChatMessage;
+import org.bukkit.entity.Player;
+import org.bukkit.event.block.SignChangeEvent;
+// CraftBukkit end
+
+public class TileEntitySign extends TileEntity implements ICommandListener { // CraftBukkit - implements
 
     private static final Logger LOGGER = LogUtils.getLogger();
     private static final int MAX_TEXT_LINE_WIDTH = 90;
@@ -100,7 +110,7 @@
     @Override
     protected void saveAdditional(NBTTagCompound nbttagcompound) {
         super.saveAdditional(nbttagcompound);
-        DataResult dataresult = SignText.DIRECT_CODEC.encodeStart(DynamicOpsNBT.INSTANCE, this.frontText);
+        DataResult<NBTBase> dataresult = SignText.DIRECT_CODEC.encodeStart(DynamicOpsNBT.INSTANCE, this.frontText); // CraftBukkit - decompile error
         Logger logger = TileEntitySign.LOGGER;
 
         Objects.requireNonNull(logger);
@@ -119,7 +129,7 @@
     @Override
     public void load(NBTTagCompound nbttagcompound) {
         super.load(nbttagcompound);
-        DataResult dataresult;
+        DataResult<SignText> dataresult; // CraftBukkit - decompile error
         Logger logger;
 
         if (nbttagcompound.contains("front_text")) {
@@ -179,6 +189,7 @@
             this.level.sendBlockUpdated(this.getBlockPos(), this.getBlockState(), this.getBlockState(), 3);
         } else {
             TileEntitySign.LOGGER.warn("Player {} just tried to change non-editable sign", entityhuman.getName().getString());
+            ((EntityPlayer) entityhuman).connection.send(this.getUpdatePacket()); // CraftBukkit
         }
     }
 
@@ -198,6 +209,25 @@
             } else {
                 signtext = signtext.setMessage(i, IChatBaseComponent.literal(filteredtext.raw()).setStyle(chatmodifier), IChatBaseComponent.literal(filteredtext.filteredOrEmpty()).setStyle(chatmodifier));
             }
+
+            // CraftBukkit start
+            Player player = ((EntityPlayer) entityhuman).getBukkitEntity();
+            String[] lines = new String[4];
+
+            for (int j = 0; j < list.size(); ++j) {
+                lines[j] = CraftChatMessage.fromComponent(signtext.getMessage(j, entityhuman.isTextFilteringEnabled()));
+            }
+
+            SignChangeEvent event = new SignChangeEvent(CraftBlock.at(this.level, this.worldPosition), player, lines);
+            entityhuman.level().getCraftServer().getPluginManager().callEvent(event);
+
+            if (!event.isCancelled()) {
+                IChatBaseComponent[] components = org.bukkit.craftbukkit.block.CraftSign.sanitizeLines(event.getLines());
+                for (int j = 0; j < components.length; j++) {
+                    signtext = signtext.setMessage(j, components[j]);
+                }
+            }
+            // CraftBukkit end
         }
 
         return signtext;
@@ -250,11 +280,37 @@
         return flag1;
     }
 
-    private static CommandListenerWrapper createCommandSourceStack(@Nullable EntityHuman entityhuman, World world, BlockPosition blockposition) {
+    // CraftBukkit start
+    @Override
+    public void sendSystemMessage(IChatBaseComponent ichatbasecomponent) {}
+
+    @Override
+    public org.bukkit.command.CommandSender getBukkitSender(CommandListenerWrapper wrapper) {
+        return wrapper.getEntity() != null ? wrapper.getEntity().getBukkitSender(wrapper) : new org.bukkit.craftbukkit.command.CraftBlockCommandSender(wrapper, this);
+    }
+
+    @Override
+    public boolean acceptsSuccess() {
+        return false;
+    }
+
+    @Override
+    public boolean acceptsFailure() {
+        return false;
+    }
+
+    @Override
+    public boolean shouldInformAdmins() {
+        return false;
+    }
+
+    private CommandListenerWrapper createCommandSourceStack(@Nullable EntityHuman entityhuman, World world, BlockPosition blockposition) {
+        // CraftBukkit end
         String s = entityhuman == null ? "Sign" : entityhuman.getName().getString();
         Object object = entityhuman == null ? IChatBaseComponent.literal("Sign") : entityhuman.getDisplayName();
 
-        return new CommandListenerWrapper(ICommandListener.NULL, Vec3D.atCenterOf(blockposition), Vec2F.ZERO, (WorldServer) world, 2, s, (IChatBaseComponent) object, world.getServer(), entityhuman);
+        // CraftBukkit - this
+        return new CommandListenerWrapper(this, Vec3D.atCenterOf(blockposition), Vec2F.ZERO, (WorldServer) world, 2, s, (IChatBaseComponent) object, world.getServer(), entityhuman);
     }
 
     @Override
@@ -283,7 +339,7 @@
 
     private void markUpdated() {
         this.setChanged();
-        this.level.sendBlockUpdated(this.getBlockPos(), this.getBlockState(), this.getBlockState(), 3);
+        if (this.level != null) this.level.sendBlockUpdated(this.getBlockPos(), this.getBlockState(), this.getBlockState(), 3); // CraftBukkit - skip notify if world is null (SPIGOT-5122)
     }
 
     public boolean isWaxed() {