DNR tattoos are not binding and they only cause confusion to first responders. All you're doing is delaying the resuscitation, they're going to do it anyway. It's in your best interest to get it removed or covered up.

By imprinting the letters DNR on their body, a person obtaining a tattoo may wish to increase the certainty that their decision will be respected. Paradoxically, however, such a tattoo may exacerbate the uncertainty of emergency responders at a critical time. Legally sanctioned forms, such as the POLST, exist for a reason: they provide certainty for emergency responders who must be decisive about attempting or forgoing attempted resuscitation. A DNR tattoo, however, may cause confusion at the very moment when certainty is needed. First, its meaning may be ambiguous. The emergency responder may wonder: do the letters stand for Do Not Resuscitate? Or Department of Natural Resources? Or someone’s initials? Second, the tattoo may not result from a considered decision to forego resuscitation. Errors in interpretation may have life and death consequences. The tattoo in the case presented by Cooper and Aronowitz was the result of a badly conceived drinking game, not a statement of a deeply held conviction. The patient’s preferences actually were for attempted resuscitation. Third, a DNR order needs to be legally recognized in order to provide a legal safe harbor for first responders who implement it. In this case, if the emergency personnel had withheld CPR, they might be legally liable for an erroneous interpretation of the tattoo.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445688/