An incomplete list: R' Meir Mazuz (on Shabbat) - source R' Herschel Schachter R' Yisroel Belsky (when wearing a long frock coat to cover it) R' Abraham Twerski (source) R' Zalman Nechemia Goldberg R' Simcha Kook R' David bar Hayim R' Yehoshua Buch R' Yoel Bin-Nun (only on his suit-jacket) R' Mo...