High pressure signs........
The indications mentioned by old_heli_logger are what I might expect to see with what I would call "very high" pressures.
Other signs will be case expansion in front of the extractor groove (most folks don't have the right tools to measure this), unusual case length growth; these signs compared to factory loads fired in the same gun.
Another earlier sign would be primer pockets getting loose after only 3 or 4 loads. Some shooters/reloaders are willing to accept early loose primer pockets, and the increased barrel wear that goes with it, for a bit more velocity.............
I think some of my loading manuals have pics and text in the front of the book that show and describe some examples of "stressed" cases.