Advanced database application areas, such as computer aided design, office automation, digital libraries, data-mining as well as hypertext and multimedia systems need to handle complex data structures with set-valued attributes, which can be represented as bit strings, called signatures. A set of signatures can be stored in a file, called a signature file. In this paper, we propose a new method to organize a signature file into a tree structure, called a signature tree, to speed up the signature file scanning and query evaluation.