By Roberta Rampton WASHINGTON, Nov 26 (Reuters) -- President Barack Obama urged Americans to show generosity to Syrian refugees in his Thanksgiving message on Thursday, reminding them that the Pilgrims who came to America in 1620 were themselves fleeing persecution. "Nearly four centuries after the Mayflower set sail, the world is still full of pilgrims – men and women who want nothing more than the chance for a safer, better future for themselves and their families," Obama said in his address.