Mayflower Flag - St. George's Cross

This flag - the flag of England - was one of two ensigns which the Speedwell (carrying the Leiden Separatists from Holland to Britain) flew as it departed Delfshaven.

John Abbot Goodwin, in his 1888 book The Pilgrim Republic, writes that the Speedwell also flew the "new" Union Jack:

The hull was wrapped in smoke, through which was seen at the stern the white flag of England doubly bisected by the great red cross of St. George, a token that the emigrants had at last resumed their dearly-loved nationality. Far above them at the main was seen the Union Jack of new device.

And Azel Ames, at page 38 of The May-flower and Her Log, July 15, 1620-May 6, 1621, writes:

And so after more than eleven years of banishment for conscience' sake from their native shores, this little band of English exiles, as true to their mother-land—despite persecutions—as to their God, raised the flag of England, above their own little vessel, and under its folds set sail to plant themselves for a larger life in a New World.