[Morgeruat]

magical tattoos are essentially additional spell triggers that enemy mages get, the red wizards of Thay are famed for having perfected their use, although certain primitive mages from Chult, and other areas such as Unther (IIRC) use them as well, once the enchantment has been used however the tattos are simply normal tattoos (except in the case of some rare Thayan tattoos that grant things such as +1 to hit, infravision, etc)

Given this information, I would think enemy mages, and Cowled Wizards in particular would be slightly more hesitant to use them first thing in a battle (as an individual tattoo cannot normally be reenchanted)