Americans with PhDs beware: Telling people in Germany that you're a doctor could land you in jail.

At least seven U.S. citizens working as researchers in Germany have faced criminal probes in recent months for using the title "Dr." on their business cards, Web sites and resumes. They all hold doctoral degrees from elite universities back home.

Under a little-known Nazi-era law, only people who earn PhDs or medical degrees in Germany are allowed to use "Dr." as a courtesy title.

The law was modified in 2001 to extend the privilege to degree-holders from any country in the European Union. But docs from the United States and anywhere else outside Europe are still forbidden to use the honorific. Violators can face a year behind bars.