Shake Shack’s application to open a restaurant on the Post Road received unanimous approval from the Darien Planning & Zoning Commission Tuesday, but the major hurdle before another crucial town board recently got higher. The P&Z voted unanimously to approve the restaurant’s application to open a restaurant at 1340 Post Road, the former site of Chuck’s Steak House. But a major sticking point with town land-use officials over the restaurant’s application has always been the larger signs that Shake Shack wants — bigger than what town regulations currently allow. The largest proposed sign would be 22 inches high; town regulations now set the maximum at 10 inches. That argument is before the Zoning Board of Appeals, which recently hired a consultant to do a “peer review” on the signage proposed in Shake Shack’s most recent application.