There is no rule preventing a WFTF shooter from secondary -- or primary -- range finding using these signs. Any stadia line or "mildot" reticle can be used. And why anyone would buy a simple cross-hair reticle these days confounds me... Cross-hair reticles are not very flexible.
I bet a WFTF shooter with a scope set at 32x can "bracket" this known measurement number to within 1/2 yard on the far targets where it counts the most... who needs to focus range find?
Anyone who thinks these numbers will NOT be used for bracketing at this "WFTF Only" match is kidding themselves.