Protestants argue that baptism is only a “sign” or pledge/answer of a good conscious that one receives before baptism. The Greek word for pledge/answer in 1Peter 3:21 is “eperotema” which means to ask, inquire, appeal or request. So this pledge/answer is not because of a clean conscience but in order to receive a clean conscious.
So, it is at baptism one makes a request to God for a clean conscience and calls upon his name (Acts 22:16). “Baptism saves” (1Peter 3:21) in the sense that it places one into the new covenant. It is the last step in the conversion process where one comes in contact with salvation (Gal. 3:26-27).
Concerning baptism being only a sign, one must understand that a sign or symbol represents a reality. Romans 6:1-5 teaches us that in baptism we become a part of the reality it represents. It becomes more than just a “sign” to those who obey the gospel. It becomes a reality. So again, the “sign” represents reality and when one is baptized they become a part of that reality in which the sign represents.