COMDTINST 1000.1F allows Coast Guard members unlimited body coverage except on the head, face, neck, hands, natural hairline and inside the mouth. Narrow exceptions follow: one hand tattoo up to two and a half inches, one finger tattoo per hand, and neck tattoos that stay hidden by a crew neck t-shirt.
Coast Guard tattoo standards are set by COMDTINST 1000.1F, which covers tattoos, branding, body piercing and mutilation together. It applies to accession points, applicants, active duty and reserve members alike.
The starting position is permissive, then narrowed by location:
No tattoo, of any type, is authorized on the head, face, neck, hands, within the natural hairline, or inside of the mouth, except as described below
COMDTINST 1000.1F, para 12
The exceptions are what most questions are really about.
On the neck, the test is visibility rather than placement:
No tattoo will be visible above the uppermost edge of the standard crew neck t-shirt when viewed from the front
COMDTINST 1000.1F, para 12.a
For the back of the neck the reference point changes to the top collar edge of the tropical blue shirt. The same crew neck test governs the chest.
Hands get a size allowance the other services do not give:
A single tattoo per hand, no larger than two- and one-half inches in any direction (height/width/diameter), is authorized on the back of the hand
COMDTINST 1000.1F, para 12.c
Its position is bounded by two imaginary lines: one across the finger and thumb knuckles closest to the wrist, and one between the wrist bones. No tattoo is authorised on the palm, ring tattoos aside.
Fingers are allowed separately from the hand:
A single finger tattoo per hand, between the first knuckle (closest to the wrist) and the fingertip, on the top or side of the finger, is authorized
COMDTINST 1000.1F, para 12.d
Two administrative points worth knowing:
COMDTINST 1000.1F sits alongside the Coast Guard Uniform Regulations, COMDTINST M1020.6, which it names as its reference.