Thanks for the confirmation that it is where I remembered. And yes, I did build the Parlor.
Since I still don't find the button, my guess is that this may either be a bug with the Linux version as a whole or one with my particular playthrough. Regardless of which, I will try once more with a another new file and see whether or not I can get it to appear.
Edit (for the developers, in case they read through this thread):
I reinstalled the 0.6.2a Linux version of the game and through save editing enabled the beauty parlor in a fresh save. The button appeared for the master character without a hitch. Doing the same for the current 0.6.3a Linux version does not make the apply tattoo button in the inventory screen appear for the master character. Which I guess means that for some odd reason a flag in the Linux release of the game does not trigger.
Edit 2:
Ok, I now tested the windows version of the 0.6.3a release. Once on a native windows machine and once in emulation environment on my Linux PC. In both cases I downloaded the game separately before starting a new save (since in both cases there were no old ones), fresh in the game I then saved. then edited the save file to 'build' the beauty parlor to test whether or not the button to apply tattoos to the MC would appear as it had in the 0.6.2a version of the game. Both tests were negative for me. The button to apply tattoos did not appear. This leads me to believe that this is a general bug of the 0.6.3 branch of the game. To ascertain this conclusion, I would kindly ask vadi92 to please double check the game version you're running where the button does appear. Or anyone else to either contradict my findings or support them so the developers have a clear picture of the problem.