Police officers also should have their homes properly identified. The cop, of course. When it comes down to it, everybody should be identified by yard sign, uniform, tattoo, or whatever it takes. Now I'm repeating myself. Most importantly, it will encourage vigilantism.
Sex offenders are easy marks to begin with.
They're quite often timid. Forcing these pathetic souls to humiliate themselves is sadistic and certainly invites trouble. There is a reason why the practice of branding criminals was abandoned centuries ago. In this case, the yard sign will hurt everybody who lives in the house, not just the convicted sex offender. And we can only imagine what it will do to real estate values.