Here is the exact MAINE STATE Statute updated August 2010:
§2001-A. Threatening display of or carrying concealed weapon
1. Display or carrying prohibited. A person may not, unless excepted by a provision of law:
A. Display in a threatening manner a firearm, slungshot, knuckles, bowie knife, dirk, stiletto or other dangerous or deadly weapon usually employed in the attack on or defense of a person; or [2003, c. 452, Pt. N, §2 (NEW); 2003, c. 452, Pt. X, §2 (AFF).]
B. Wear under the person's clothes or conceal about the person's person a firearm, slungshot, knuckles, bowie knife, dirk, stiletto or other dangerous or deadly weapon usually employed in the attack on or defense of a person. [2003, c. 452, Pt. N, §2 (NEW); 2003, c. 452, Pt. X, §2 (AFF).]
[ 2003, c. 452, Pt. N, §2 (NEW); 2003, c. 452, Pt. X, §2 (AFF) .]
2. Exceptions. The provisions of this section concerning the carrying of concealed weapons do not apply to:
(I have eliminated the text for firearms as not relevant to this thread. RayseM.)
C. Knives used to hunt, fish or trap as defined in Title 12, section 10001; [2003, c. 452, Pt. N, §2 (NEW); 2003, c. 452, Pt. X, §2 (AFF).]
So, not being an attorney - I think "threatening manner" & "Wear under the person's clothes or conceal about the person's person" are the key phrases. I have not found any notation about knife blade length being a consideration. If you carry a hunting license - I think (my experience supports this) - you will be left alone during various hunting seasons if you are visibly wearing a sheathed knife having breakfast at a diner, but would likely run into trouble wearing the same rig while having dinner at a restaurant in Portland, hunting license notwithstanding. I'd like to say that common sense should prevail, but I also think that the wrong cop in the wrong mood could make your life miserable as regards knife carry. I think the only way to be more clear on this topic is to discuss the issue with a state trooper or game warden. Likely get 2 interpretations. I need to have such a discussion some day. I'll get back to you if I do.