Locals in both places wear nothing but LL Bean; they talk funny, and there's nowhere to park. It's no wonder people often get Maine and Boston confused.
The easiest way to tell them apart: Beacon Hill is in Boston, while Munjoy Hill is in Maine [Portland, to be exact]. If you STILL can't figure out where you are, just take a look around. If you see a store full of quirky plush toys called Softheads, and baby t-shirts and bodysuits with line drawings of a deer playing the accordion or of a squirrel playing a snare drum, the store's called Ferdinand, and you're in Maine. Voila, mystery solved.
Squirrel baby t-shirt (American Apparel organic), $15 at Ferdinand [ferdinandhomestore, via dt reader molly]