One of my car rear tires has a different MAXIMUM PSI than the rest 3 , is that a problem?

Manufacturer's recommended tire pressure is usually printed on a metal tag on the door post in the driver's door. Safe? No idea. I wouldn't worry too much if driving short distances at slow speeds, but I'd probably get all 4 tires to match before getting on the freeway. But if you have no alternative but to make the drive, then I'd make sure the odd tire wasn't too different in structure, then inflate to whatever the automobile manufacturer posted inside the driver door. And check them periodically for wear. Good luck,

The markings on the tyres is the maximimu for the brand of tyre. Inflate them to the vehicle specification and it will be fine. No, there's no misunderstanding, I know what you're asking and the answers the same. Inflate them to the car manufacturers specification and you're fine.

This markings within the tyres could be the maximimu for your brand name associated with tyre. Fill these on the motor vehicle specification and it will likely be very good. www.12vcity.com

The fourth tyre is obviously a cheaper brand which cannot support the same pressure (or weight, probably) as the other three. The fact the spare is the same max pressure suggests that the odd one on the car was probably the spare at some point, so check the current spare isn't punctured or illegal tread (may be that it was puncture repaired). For best driving grip and response, you should only ever fit matching tyres per axle (front pair or back pair), though the rear wheels of most cars (unless it's RWD or 4WD) does little more than roll along to support the back of the car!