For most semi-auto pistol rounds, the best indicators I have found are recoil and distance case are thrown compared to factory loads with the same weight bullet.
Many .45s have a LOT of unsupported case (feeding reliability vs case support, with the low pressure making them think that case support is not needed), so any bulging is also sure sign you are OVER pressure.
I always wondered about magazine writers who warn that XXX cartridge is made with thin case walls and won't hold pressure. If the case is supported properly, all the case knows is pressure on one side and solid steel on the other and thickness doesn't matter. Thus, I always figured it was the strength of the cylinder/gun and NOT the strength of the .45 Colt case that limited pressure.