Haha, that was a pretty funny story. So, now, a few corrections, which I will try to put into bold font.

One story

One day, my brother and I drove to bathe in the river. The place was beautiful: clear water, green forest around, soft yellow sand. But we saw a sign that said "no entry" for our car, but we ignored it.

After a good rest, we had to return. We remembered a police car at the nearest intersection. They had seen us, of course. And they would have taken us on our way back (if I understood correctly, of course back way can also be a small road)

But we saw, that sign "no entry" was not fixed and we took it down easily and threw it into the green trees near the road.

The police stopped us. Why did you violate the sign that says "no entry" ? Where was the sign ? We asked... They have proposed to go and check it. Ok, we had returned to place where road sign should have been (here must is almost like a deduction, but you, who took the sign down knows that it won't be there...not a deduction vs should have been=but it wasn't), together with policeman. And we all saw only empty place....
Policeman said: "It was removed, again..." But his voice was very unhappy and sad.