Identification is an important part of what the Coroner's Office does. We want to be certain that the decedent that we think is the decedent is the decedent we think they are. Many activities go in to identification and range from the "simple" visual identification to the "complex" DNA profile match.
Many times identifying marks on the body provide important information in assisting to know who is who (or is it who is whom?). Tattoos are certainly among the most obvious of body "marks". Unique tattoos have proven to be very useful in our work and I recall at least one case in which it was the most crucial bit of information we had available in identifying an individual.
While many individuals (particularly parents) would likely object if I were to recommend unique tattoos for everyone, to assist us in post-mortem identification, I wouldn't be adverse to such a recommendation. So, if you get a tattoo, make it a unique tattoo, and make sure others know about it if you want it to assist in post-mortem identification.
(By the way, I saw some pretty neat ones in a book--500 Tattoo Designs by Henry Ferguson-- we were looking at after supper tonight.)