Hi Les 

There are multiple ways you could make a credit note stand out from the invoice,  showing the sign or turning the wording Credit note Red are just a couple . 

you may be better logging a case with the Report design team about the different options.  in sage goto help then help centre type case in the search option to get a video on logging a case for support. 

As for the minus sign, when you edit the layout and click on an item that you would expect to return a value like net, tax or in item that starts with the word foreign. you then look for the propertied on the right and make sure the sign is sed to signed and not unsigned. 

If properties aren't showing then click view in the top left then properties  

repeat that for each value/data field

I hope that helps 

Lee