If you install lightdm on distributions other than Ubuntu you may want to have the Ubuntu logo in the lower left corner removed or altered. This can be done easily by editing the original picture file which is located in /usr/share/unity-greeter/ (remember to open the folder as administrator, or do it right from a terminal as root).
The file you want to edit is logo.png. You can either rename it, so it doesn't show up on login anymore (for example, rename it to logo.png.bak - if you want it back, just remove the new extension again), or edit it with a graphical editor right away so that it reads something more appropriate to your distribution or login screen.
Change Ubuntu logo on lightdm login manager
Bad advice! Come the next package update your changes will simply be overwritten. Google on to find out how to do the job properly.