Blazon: Per fess I per pale gules a Maltese cross argent and chequy of fifteen azure and the second, II of the third a sword in bend and a spear in bend sinister, points to the chief, surmounted by “Mambrino’s helmet,” all of the second.
This depiction is not particularly accurate; the original blazon specifies that the lower half of the shield should be azure, with argent charges. Inexplicably, the official site of the city uses a very similar depiction as that seen here.
The final charge is a reference to an incident in the Cervantes novel Don Quixote de la Mancha. The titular character sees a barber caught in the rain and wearing a basin as an impromptu hat, and declares this basin to be the fabled helmet of the legendary Moorish king Mambrino, which is supposed to make the wearer invulnerable. The novel also makes reference to the town, and a local legend holds (without much proof) that Cervantes was once imprisoned in a cave near the town.