Tattoos are not really regarded highly by the general public in most of the civilised nations. Aliens, on the other hand, are fairly acceptable. These facts make alien tattoos have a peculiar taste of their own. If you are making tattoos for your own pleasure then there are as many designs to choose from as there are stars in the sky, but if you aim to become a head turner in the positive sense of the word, a lot has to be taken into consideration: the social codes your society adheres by etc. You can choose either UFOs or Martians or Venusians or anything that of your choice.