Join Date: Nov 2005
Location: SIN / CNX / SFO
Programs: UA GS, SQ PPS, Hyatt Globalist, Marriott Titanium, Hilton Diamond, Accor Gold
Posts: 1,253
At least for Japanese passports, it's just the regular oval entry stamp / rectangular exit stamp—nothing special/unique about it, other than that there's no corresponding visa sticker/TWOV stamp.
Same as how there's no special "visa-free" Schengen stamp.