Stallone admitted he used steroids, that's how we know. That's the ONLY way we know. If Stallone were 230lbs and ripped, THEN you could say he obviously uses steroids.
You are truly clueless. A drugged physique just looks different. There are a ton of signs. Like swelling of the cranial muscles, disproportionate hypertrophy of trap/shoulder area, skin texture and body fat pattern and even things small things like sweating pattern. You can tell a heavy juicer without even seeing his body just by looking at his face. BTW, Stallone never admitted to steroid use back then... he talked about using a special amino acid supplement.
Take a look at this fool. If you can't tell he's on steroids you're clueless. He's small by bodybuilding standards but there's NO doubt he's on the juice.
Same thing with Mickey Rourke in The Wrestler and numerous previous movies. Put his stats on paper and it's not obvious he's a juicer but once you see him it's very obvious.
Here's another
