Have to assume its NeW England, it doesn't make sense to me either, you'd think NEP would be the abbreviation seeing as the Jets are NYJ, Giants are NYG, etc. There isn't a good 3 letter abbreviation for New England so why not toss the team name in it like a few others do.
Most likely to keep with 3 letter abbreviations. San Fran-SFO Green Bay-GNB etc. Like the Post Office using 2 letter abbreviations for states.