IBGE Tile Layer
A tile layer was generated by Thiago Santos based on IBGE's map data in the PDF format. Mapbox kindly hosts this layer, which can be used in iD or JOSM. Check out the code repository IBGETools for more information about how this tile layer was generated.
There is no formal license, IBGE stated that all data in their site are "public domain with attribution required", so it is necessary to add the tag source=IBGE to all data from these layers.
How to activate the layer
JOSM already has this preset selectionable when you download an area in Brazil. All you have to do is activate it, by going in Imagery > IBGE Mapa de Setores Urbanos.
It also helps to have activated a style that highlight streets that have no names. You can activate it by going in Edit > Preferences... > (third icon) > Map Paint Styles > Streets Have No Name (left panel) and clicking the right arrow between the panes.
On iD Editor, you have to enter Background imagery configuration, and add a custom imagery with the following URL:
First word in capital letters
You will notice that the map has all the names in capitals. The general rule is to copy all the words with the first letter as capital, such as Rua Teste instead of RUA TESTE.
Except for Articles (connectors)
If you find a road that has an article on it's name (de, do, da, dos, das) you can leave that in small letters, such as Rua de Teste instead of Rua De Teste.
Some street names may have words with diacritics (such as Rua São Cristóvão instead of Rua Sao Cristovao). This can be hard for a foreigner to recognize. You can copy the words and make a google search to check for its spell, leave without diacritics and hope that a local mapper would correct it (name without diacritics is better than no name, after all) of simply skip it.
Names such as NAO NOMEADO, SEM DENOMINACAO, PROJETADA and SEM NOME means that street is unnamed, and should either be left blank and positively be confirmed as unnamed by setting the tag noname=yes.