There are many books about wayfinding systems.
Among them, one of the best and more detailed is for sure Signage Systems & Information graphics.
A lot of matters are explored in this book from the german designer Andreas Übele. What interests us the most : Typography and pictograms.
Indeed, these are two essential weapons to master perfectly to succeed a signage system project. Signage Systems & Information graphics teaches it pretty well, especially for what is about typography. Many well known fonts are introduced (or reminded), and compared in a very relevant way.
« Look at the lower-case ‘a’ in Akzidenz Grotesk Light : the curving base of the stem is too long, and the counter is too broad. This may be why Akzidenz is better suited to longer texts than Helvetica, as these details hold the letters together like serifs. »
According to Übele, the choice of a font depending on what it will be used to, is extremely important (« If in doubt, use Akzidenz Grotesk »).
The book gets also onto grid for wayfinding systems (« Never ever work on signage without a grid! »).
Color, very important part in this domain of graphic design, is also got onto in a very detailed way, describing advantages and inconvenients of use of many common colors.
In addition to this revision of basis of visual communication, several precisions for many potential places for signage systems (airports, museums, schools, library, public spaces, etc.), with lots of pictures (mainly german and european projects). Finally, you should have a look on the bibliography of this book, which contains lots of good books about typography.