The login screen on your Mac is perfectly functional as it is, but if you want to spice it up a little bit, blogger Jacob Salmela shows you how to customise the login screen with a logo of your choosing.
To do this, you can use a tool like the previously mentioned Deeper, but if you don't want to install a whole program just for a simple tweak it's easy to do manually. All you need is a PNG that's 428 X 248. Then, you'll need to save it as four different files. Here's Salmela's instructions:
You need four copies of this file, and they need to be named:
Once they are named correctly, just drag them into the following path:
and then choose to replace all of them.
That's it, log out, and you should see your new logo. Head over to Salmela's site for a few sample images and instructions for making your own.
OS X Mavericks Change the Login Window Icon or Wallpaper [Jacob Salmela]