Problem with that idea (nice though it is):
We don't have a 3 (or 4) foot law in New York State, so municipalities would never put up a sign stating that.
If a cyclist was ever hit there would be lawsuits all over the place with whoever put the sign up, probably taking the blame.
Advocacy | Safe Cycling and Cycling Jerseys | 3FeetPlease.com 1MetrePlease.com
Nice idea though.
I think this is a pretty good option:

From: Chuck Dominick <chuckdominick@PROTECTED>
To: Cycling Club <occ@PROTECTED>
Sent: Monday, August 31, 2015 10:01 PM
Subject: Re: occ: 'New Study Confirms: “Share The Road” Is a Problem'