In the US, The Freedom from Religion foundation offers a “Debaptism Certificate”. The picture is too small to see, so to help you out, the text reads …
I, having been subjected to a Christian baptism before reaching an age of consent, or having submitted to baptism before embracing freethought and reason, hereby officially renounce that primitive rite and the Church that imposed it. I categorically reject the creeds, dogmas, and superstitions of my former religion, particularly the pernicious doctrines of ‘Original Sin’ and damnation.
“I further denounce as an affront and defamation to humanity the false and demeaning belief that any baby is born with ‘Original Sin’ and must be cleansed of it by baptism. From this day forward, I wish to be excluded from any claims of religious affiliation or membership based on baptismal records.
Why would you take this step? Well, perhaps one good reason is to remove yourself from the statistics that are used by the churches to demand more privileges, and perhaps also to break the formal connection with institutions that are counterproductive to peace, harmony and common sense. Another thought is to simply “come out” within your community, or to initiate a public debate. Evangelical noises are getting louder and louder, so its a way to push back and take a stand.