Hey,

There is no strict rule as to whether a candidate with permanent tattoo is allowed to take the exam or not, but it might cause you a problem if the invigilator objections and takes the tattoo  as a way of cheating, thus to avoid any chaos reach 1 hour before the reporting time and cooperate with the checking committee and convince them that it is nothing related to cheating without argument. They will understand and you will be allowed to take the exam

I hope this helps.

All the best!