Castagno's signature directories are the best available and this one is no exception. When researching or verifying old master or any other signatures, check his books first.

New York-Pennsylvania Collector

Art histories and collectors will find this volume of artists' signatures of value in researching the artwork of the Old Masters.

American Reference Books Annual

This work is the only signature book focusing on signature examples of Old Master paintings, drawings, prints and other art work. There are 2,700 signature examples of 1,700 artists...Listed in alphabetical order, each example includes the data on the artist's nationality, birth and death dates, bibliographic information, and auction data... It is well researched and very much needed by anyone who has any interest in old master art work or may expect to own or purchase old paintings. It is well recommended.

The Antiquer's Guide

...a basic guide for public library and academic collections...

Reference and User Services Quarterly

...a solid reference tool...

Antiqueweek

...provides clear and accessible access to information on an important element of innumerable important works of art...belongs in serious art history collections.

Rettig On Reference