The reason they specify the black chequering areas is because they are free of reflective or coated areas that can impede signal, plus they won't get damaged.  

Umm, now I don't know whether we have the exemption or not. Registered online today to check it out and even though it shows the state of our request as Validado when we try and print off the proof there is no information on it. Or, have I got it wrong and you only need to print off the page and sign it when you are sending in your certified documents? Help please!  

Open online account, click on SCUT Positva,

then Estado do Pedidoas as you say says Validado,

click on Visualizar/Imprimir Comprovativo

Print off sign and send with documents, recorded at least  

Thanks Canoeman but there is no information on the comprovativo to sign. Now I've looked more carefully through the documents we got when we were buying the box in the post office I see there is a copy of our signed Pedido de Discriminação Positiva so I assume it has already been sent to Via Verde along with the copy of the log book. I think we'll wait and see if we get charged when we use the motorway.  

If it's a new purchase then it's all done there and then, it's only old (pre SCUT tolls) existing Viaverde a/c that should need to apply and complete forms for exemptions.  

Great, thanks