The Fifth Amendment is part of the Bill Of Rights which are a set of amendments to the Constitution Of The United States. The Fifth Amendment says that people cannot be required to testify against themselves. The Supreme Court ruled that the Fifth Amendment protected a man from being forced to register an illegal gun in the case "Haynes versus United States". That Supreme Court ruling has been cited in other cases such as "Weyer versus United States" and "Reed versus United States" so the precedent is well-established.
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb, nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use without just compensation.