This is the official, legit, 'may paper trail' kind of status. It can mean someone was formally appointed to a position, like a 'nombrado' director in a government agency. It can also mean someone is so famous (or infamous) for something, they are 'nombrado' for it—like a 'nombradong magnanakaw' (renowned thief). It's got that old-school, slightly formal, Spanish-era vibe.