All traffic signs have radiused, or rounded, corners. Once the corners have been rounded the original "sharp" corners are referred to as Phantom Points and are indicated on a spec drawing by a sharp dotted line extending out beyond the radius of a sign blank. This phenomenon is least noticeable on rectangle, square and diamond shaped signs, and the most dramatic on triangle and pennant-shaped signs. The drawings below illustrate the effects of Phantom Points on three of these shapes.

For example, a 30" triangle (shown far left) will measure 30" along its side when the Phantom Point is included, but the same triangle measured after the radius has been applied is smaller than 30". Although they might seem unusual these measuring methods are an industry standard! 

We often hear from customers who think they need a 24" Yield sign, but actually need a 30" Yield sign since they both measure slightly smaller than their designated size. If you're unsure of what size to get it's generally better to err on the side of a larger sign than a smaller one, especially if the sign in question is a triangle or pennant shape.