Edit – was writing what Jérôme just explained.
I heard a comment that a particular instructor will not utilize sign offs. If that is the case perhaps not the best instructor for a given individual. Choose another instructor who will offer sign offs appropriate to skill level. Personally I agree with the concept of sign offs. As a helicopter CFI it was up to me when to solo a student. Some were skilled and safe at 8 hours. Others at 20 hours. Overall it sounds like a disagreement with an instructor, not a reason to change safety rules. If a student has not been given a sign off it may be that his instructor is erring on the side of safety until the student has shown more improvement.