The only thing you can do to your Lockscreen is all those logos available in DIY app in Nokia store...

Like I have a icon of a Lock on my Lockscreen, making it feel to others, that my N9 is currently locked... its just a icon...

There are whole lots of icon with this app to stick to yr Lockscreen..
(Also the Batman like yours)

Additionally you can put any Text you want on your Lockscreen with BillBoard app on store... Besides regular options of Date/Song name/Battery usage, etc, it also has option to put Text you want.. for instance, you type 'Dont touch my phone'. this will appear on your Lockscreen... Quite interesting...

Let us know what more can u do with Lockscreen or Standby screen....