The Android app LockScreenMessage lets you show any message you like permanently on your lock screen.
It can be especially useful for showing contact information in case the device gets lost.
LockScreenMessage has a light and a dark theme that adapts to the system settings.
The app was tested manually. I could not find any bugs, but there still may be some.
Feel free to get in contact and share your experience with LockScreenMessage. Bug reports are also very appreciated.