I have a business meeting at a prison (Netherlands). I cannot find anything about piercings, but you have to put all your stuff in a locker and go through a screening door. Would a titanium cage trigger the alarm? I am doing a long streak, but for this I can take off if needed. Hopefully someone have a clue about this.
Read the fine print on prisons. You consent to a cavity search if they feel it is necessary for the security of the facility. Taking it off for a short while might be smart.
Been in and out of courthouses and jails on business with a SS cage, no problem (wanded once and had to explain "jewelry"). But gotta admit, I would be more nervous going into a prison...
I just reached out to a friend of mine who reacently worked at one in NL. Hope to provide you with info soon!