bsa,
The problem with traditional pressure signs is they often don't show up until around 70,000 PSI, or even more. Which is why I tend to reply far more on the chronograph than anything else: If the load gets significantly more velocity than various sources indicate it should, then the load is probably over the SAAMI maximum average pressure, regardless of what the primer looks like, or whether there's no ejector-hole imprint on the case head.
Of course, some people would suggest that as long as there aren't any "pressure signs" the load is safe in that rifle. And it is--at that pressure. But pressure changes with temperature, and even the most temp-resistant powders all tend to gain velocity (and hence pressure) as the thermometer rises above about 80 degrees. All of which is why SAAMI tends to be somewhat conservative in their pressure specs.
