You cannot lose your copyright other than by your signed agreement. But look out for the term "work for hire". That specifies the company owns your work. If

You cannot lose your copyright other than by your signed agreement. But look out for the term "work for hire". That specifies the company owns your work. If you are a regular employee then the company owns your work. In the US the determination of whether you are a consultant or employee is determined by the "twenty factors", also known as the "twntry questions".