At the official website, you can see a flag behind the mayor, light blue with what looks like the top of the coat-of-arms. No clue about the presence or not of letters on the flag. We may suppose or hope not, since Iquique is already written on the shield. From this image I concluded Iquique has a flag, although it is hard to tell if its accurate enough. Olivier Touzeau, 9 August 2006
The photograph online at https://upload.wikimedia.org/wikipedia/commons/b/be/Universidad_Arturo_Prat_de_Iquique.jpg shows two flags flying atop a building at Arturo Prat University in Iquique. The flag on the right appears to be the flag of Iquique commune, showing the municipal coat of arms at the cente r of a white cross on a light blue field. The dark flag on the left, I honestly have no idea what that one is. This photograph appears to confirm the graphic that Wikimedia user B1mbo posted to that site on 16 April 2009 (see https://commons.wikimedia.org/wiki/File:Bandera_de_Iquique.svg). Randy Young, 31 August 2018
the official flag of Iquique is plain light blue with the coat of arms in the center and the name of the municipality. It has been observed only in official use with the mayor and the municipality.
a variant with a white cross has been spotted on the university building. Maybe this design has been prescribed for other uses.
image by Randy Young, 31 August 2018
based on an original image by Wikimedia user B1mbo, posted 16 April 2009
The photograph online at https://upload.wikimedia.org/wikipedia/commons/b/be/Universidad_Arturo_Prat_de_Iquique.jpg shows two flags flying atop a building at Arturo Prat University in Iquique. The flag on the right appears to be the flag of Iquique commune, showing the municipal coat of arms at the cente r of a white cross on a light blue field. The dark flag on the left, I honestly have no idea what that one is. This photograph appears to confirm the graphic that Wikimedia user B1mbo posted to that site on 16 April 2009 (see https://commons.wikimedia.org/wiki/File:Bandera_de_Iquique.svg). Randy Young, 31 August 2018
From what we find online we may conclude that:
the official flag of Iquique is plain light blue with the coat of arms in the center and the name of the municipality. It has been observed only in official use with the mayor and the municipality.
a variant with a white cross has been spotted on the university building. Maybe this design has been prescribed for other uses.