There is no SAAMI specification for "+p+" ammunition.
But, if your loading ammo above recommended load data listed in published reload manuals you should be looking for over pressure signs. Flattened primers, Pierced Primers, bulging cases, Cratered firing pin strike, Enlarged primer pockets to name a few.
You don't need a gun exploding to show you there are issues with over pressure. Although that can be one of the signs if you shoot 1 hot round that your gun can't handle.
Edit: I should add that if your reloading any ammo you should be looking for these signs as well, even if it's within the published data.