Accuracy - Accuracy is best at certain pressure nodes. Usually 1 at near min charge weight and one at near max. So, when working up a load, bad accuracy is a sign.
Velocity - If you have a 230gr 45 ACP load running 1000 fps, it is likely TOO hot. 850 is std hardball, 770 softball, 900 warm, 950 is +p sd ammo in general. This varies by powder. Know what too fast is for your powder.
Sd - Standard deviation when working up a load. This normally get it's best at max safe load, then opens up. Bigger numbers near max manual charge indicate the load is too hot. Usually, I get an ok sd at min, then it gets worse, then while approaching max, sd becomes the smallest. Over max, it gets bigger again.
Recoil - Factory ammo is nearly all max pressure or over in the case of +p. If your loads recoil more than factory fodder, it probably is too hot.
Primer Drag - on many guns, hot loads have some primer tip drag against the primer. Some is ok. Learn how this looks on factory ammo and set that as a visual max.
Primer reading - low pressure primers can be read too. Look at the edge before and after firing. Compare to same brand factory ammo for max limit. Also look in the tip dent. Look at the way the pin tip radius gets pushed out of the primer by the anvil. That is a key pressure sign.
Other brass marks - watch extractor marks, case heads being hard to fit in shell holders, loose primer seating
Also, there is:
safe pressure forever
safe pressure for a few thousand rounds, but will ultimately break something +p
safe pressure for a few rounds, but really is a proofing load
unsafe and part of your barrel is in your safety glasses and your mag shot out so hard it dented your steel toes!
Try to operate at safe.