Traveling to Vietnam? Here's an interesting detail: Vietnamese customs don't stamp Chinese passports. Instead, they issue a separate 'loose-leaf visa' and stamp entry/exit marks on that paper. This is related to the South China Sea sovereignty disputes between China and Vietnam (and several other countries). Did some digging—there were maritime armed conflicts between China and Vietnam in 1974 and 1988. Since 2012, China started using a new version of its electronic ordinary passport, which features a background map of China that includes the 'nine-dash line.' Vietnam believes that stamping or attaching a visa directly onto the Chinese passport could be interpreted as acknowledging the sovereignty claims represented by that map. As a result, Vietnam has long adopted the loose-leaf visa method, stamping entry/exit marks on a separate sheet instead of the Chinese passport. Vietnam is probably the only country still using this approach for Chinese passports.