Following in the wake of the recent updates to the Army's body art and tattoo policies, the Marine Corps has toughened up their guidelines around tattooing. The bottom line is if you wish to have a long military career with advancement, you need to skip the tattoos. Regulations passed in 2007 banned the dense and comprehensive tattooing known as "sleeve tattoos," where the arms are inked solid from wrists up to the shoulders. For Marines who happened to already have tattooing that fit that description, those tattoos were grandfathered in so that people didn't have to face discipline or discharges due to the sudden change in the rules.
For those with those sleeve tattoos, certain types of assignments and postings are prohibited. Heavily tattooed Marines will not be allowed to work as recruiting officers and are barred from security guard assignments. The grandfathered tattoos however are included in the newly-updated regulations whereby enlisted Marines with sleeve tattoos are now allowed to become commissioned officers. While those soldiers will still be eligible to earn enlisted promotions, they will not be able to pursue a commission unless they get the tattoos removed. Banned tattoo locations include any tattooing on fingers, hands, wrists and inside the mouth, along with on the neck, face or head. Any tattoos that are visible when a Marine is wearing PT (physical training aka exercise) gear must not be larger than a hand with fingers spread or closed.
Corps officials have said that these rules have been in effect and the new regulations are just a matter of clarifying and clearly spelling out the guidelines so as to avoid any misunderstanding and to better define any possible interpretations. Some tattoo shops located near Marine bases have posted copies of the rules, and will deter recruits from getting ink that violates the rules, while others say the responsibility is up to the Marines themselves.
To learn more, you can read the Marine Corps Uniform Regulations in the section titled Personal Appearances, or the 2008 Special Duty Assignment Policy.