It presumably means the person who has it is local to, comes from or has some other strong affinity with southwest Alabama, where that code is from.
It also means they haven't thought too far ahead into the future, as there's no guarantee that code won't change in the future and leave them with an out-of-date tattoo!
Ethiopia
The country code and area code of Gonder, Ethiopia is 251, (0)58.
The country code and area code of Kavala, Greece is 30, 251.
The country code and area code of Goudji, Chad is 235, 251.
The country code and area code of Harar, Ethiopia is 251, (0)25.
The country code and area code of Malanje, Angola is 244, (0)251.
The country code and area code of Qom, Iran is 98, (0)251.
The country code and area code of Donduseni, Moldova is 373, (0)251.
The country code and area code of Dolj, Romania is 40, (0)251.
The country code and area code of ÌÉlvdalen, Sweden is 46, (0)251.
The country code and area code of Dessie, Ethiopia is 251, (0)33.
The country code and area code of Shashemene, Ethiopia is 251, (0)46.