String outstr = event.original.toString() + " : ";
		if(Minecraft.getMinecraft().theWorld.isRemote)
			outstr += "client";
		else
			outstr += "server";
		System.out.println(outstr);

-----------------

[20:35:51] [Client thread/INFO] [STDOUT]: [arcaneStorageAndSecurity.PlayerEventHandler:renderOverlay:18]: 0xtile.stone@0 : client
[20:35:51] [Server thread/INFO] [STDOUT]: [arcaneStorageAndSecurity.PlayerEventHandler:renderOverlay:18]: 0xtile.stone@0 : client