The Use of Capitals
http://www.tc-forum.org/topicus/ru28theu.htm

Gaviero-Villatte, Elisa
TC-FORUM
2000

Abstract:

The question to the list-subscribers was I am looking for studies dealing with the difference between small letters and capitals. Are small letters easier to read? In France, road signs are written in capitals but it is not the case in the US or Canada.