Singaporeans have a solution for this: they understand a pack of tissues or a business card on a table to mean "reserved": http://3.bp.blogspot.com/-fXrUY-3NMjc/Tspv4vvgSDI/AAAAAAAANv...

But what if they have no tissues at hand? Using a smartphone is also fine, because there is so little crime: http://www.mrbrown.com/.a/6a00d83451b52369e2019aff6d022f970b...