Sometimes people ask me to send them a list of literature on linguistic landscape. For an introduction to the field and for further references I would advise the following publications.
Backhaus, P. (2007). Linguistic Landscapes: A Comparative Study of Urban Multilingualism in Tokyo. Clevedon: Multilingual Matters
Gorter, D. (ed.) (2006). Linguistic Landscape: A New Approach to Multilingualism. Clevedon: Multilingual Matters
Landry, R. and R.Y. Bourhis (1997). Linguistic landscape and ethnolinguistic vitality: An empirical study. Journal of Language and Social Psychology, 16, 23-49
Shohamy, E. andD. Gorter (eds) (2009). Linguistic Landscape: Expanding the Scenery. London and New York: Routledge