After Spain and Portugal's Inquisitions, Jews who forcibly became “New Christians” and "Crypto-Jews, formed themselves into tightly-knit groups of “friends” and family, making it understandable that once you get to your family tree you should see other Jewish names. Watch for the point when they began Anglicizing their names. Look for even the slightest change of spelling and especially any surname change. In the 1700 and 1800s, cousins sometimes married. This could be a clue; Jewish families wanted their children to marry other Jews. No doubt, there were situations where the young couple may have been unaware that they were Jewish, yet both sets of parents knew.
Suellen Ocean is the author of Secret Genealogy a how-to for tracing ancient Jewish ancestry and Secret Genealogy II, Uncovering the Jewish Roots of Our Christian Ancestors, both available at Amazon, B&N and Ocean-Hose. http://www.pacificsites.com/~oceanhose/