1. Maine has permitless carry for anyone over 21 who can legally possess a firearm. Active Military and National Guard can carry at 18.
2. Maine does not honor all other states permit/licenses. Their law on how they honor other states did not change. It reads:
25 MRSA §2001-A, sub-§2,
F. A handgun carried by a person to whom a valid permit to carry a concealed handgun has been issued by that person's state of residence if that person's state of residence honors a permit to carry a concealed handgun issued under this chapter; [2015, c. 144, §1 (RPR).]
3. It makes a difference on who Maine honors as the Maine State Police state that by their laws Permitless Carry is not allowed in Maine State Parks. Their Parking Lot Storage Law does not apply to those carrying under Permitless Carry and carrying a defensive handgun while bow hunting requires a permit. These three items require either a Maine or Non-Resident Maine permit or a PERMIT THEY HONOR.
4. Now for the biggie. Arcadia National Park is the only Nat. Park in Maine. The Maine State Police who I have talked to via email and phone more than once (Lt. Ireland) stated and their website states it
http://www.maine.gov/dps/msp/licenses/weapons_permits.html
that A MAINE RESIDENT OR NON-RESIDENT permit is required to legally carry in Arcadia Nat. Park. Those carrying under permitless carry or even with a permit they honor is not valid in Arcadia Nat. Park. The Nat. Parks go by the rules of the states they are in and if Maine says this is what it takes to carry in their Nat. Parks then that is what the National Park will go by.
5. Maine laws have set a trap for those non-residents carrying in Maine. Arcadia Nat Park is a destination point in Maine. Many non-residents go to Maine just to visit Arcadia. Permitless Carry in Maine works in most of the state but there are places it doesn't for those without a permit and even places that are just off limits to those without a Maine permit.
More information can be found here:
http://www.handgunlaw.us/states/maine.pdf
6. I forgot. Also if carrying under permitless carry in Maine you have a duty to inform immediately any Police Officer that approaches you on any official business. Those with a permit do not have the duty to inform! I don't make the laws I just report them!