Tattoos

Possibly:
(a) to help ensure they don't reoffend upon release
(b) because some will be prisoners of conscience and / or convicted of no-harm crimes (e.g. drug possession)
(c) because those in prison are disproportionately from disadvantaged groups and non-white communities, indicating systemic bias which needs correcting

that is a load of bollocks and even it were true how would a tattoo circus help matters?

There is no location the day before it is on, unless you call some dodgy mobile which reminds me of a misspent youth calling numbers for squat raves. This also leads me to believe it has been (badly) organised by a bunch of crusties. If it's close to hackney i might still go though...

as long as there is no psy-trance ;)