WASHINGTON, Dec 5 (Reuters) - A growing number of Americans are donning the keffiyeh, the distinctive patterned scarf that's closely linked with Palestinians, to demand a ceasefire to Israel's attacks on Gaza or to signal their support for Palestinians. Sales of the scarves have jumped since the Israel-Hamas war began in October, U.S. distributors say, even as keffiyehs have been forcibly removed by security forces at some protests and wearers report being targeted for verbal and physical abuse. "It was like a light switch. All of a sudden, we had hundreds of people on the website simultaneously and buying whatever...