how would I know if the plane I am about to fly in has exceeded the G force/structural limit with other flyers?
Aside from perhaps noticing a wrinkle in the skin which should not be there, sheared rivet heads, or something else apparently broken, you're not going to know.
Do planes have some sort of G force device/marker that indicates if the structure has exceeded the safe limits?
No, unless it has an accelerometer, and someone takes notes, before it gets reset.
That said, the capacity of those (and all certified aircraft) to carry high G loads is considerably more than most people expect. It will be (flaps up) a minimum of 5.7G before the aircraft becomes not flyable. I won't speak too much to the Piper, but for the 152, remind yourself that it has been said that there has never been a failure for the structure due to flight loading, of a strut braced Cessna. 5.7 G would be
really hard for most pilots to ever achieve. Having done hundreds of loops and rolls in 150 Aerobats, I have never exceeded 3.5G. I did approach 5G in the Aerobat, but I was really trying, and it's approved for it.
When doing the walk around of the 152, it is not so much the condition of the wings which should concern you in the over stressing sense, but the H stab. When you're pulling G, you're doing it by making the H stab push the tail down. In that context, in begins to make more sense that Cessna designed it so it's sitting on to of the tail, rather than hanging from, or being bolted to it.
The H stabs are subjected to G forces, careless ground handlng forces, and buffetting forces. The result is the occasional cracking of the forward ribs of the H stab, which mate to the fuselage. Losening of the rivets in the H stab is also known. Both of these are detectable by the pilot, and in their early stages do not make the plane immeidately unsafe to fly.
In general, any of these planes with no unexplained wrinkles, no sheared rivets, and nothing falling off is very likely structurally safe to fly. As for the landing gear, if the nose wheel is not broken off, or a main tire not burst, it is very unlikely that the main landing gear has been damaged by a hard landing.
During the required inspections, the maintainer knows what to look for. If they don't like what they see, you won't be flying the plane. A few "more recent" light aircraft do have an airframe hour limit (Tomahawk, I think). The much older ones were built before there was an intent to limit light aircraft airframes this way, and are just "on condition". The safety record supports this being a good way of doing things. Aircraft with pressurized fuselages are something completely different!