This is one of these "when in Rome" things. You can't compare how it's done in Sydney with how it's done in San Francisco. In San Francisco, the tip is a significant part of the staff's compensation (not necessarily just your specific server).

If you come from a place where a tip is not common or it's included as "service" and people sometimes leave a few coins, there is no other easy way.

Lots of foreign visitors @ San Francisco. Better the receipt printer spells out the tip %, but I'm not offended by the practice.

If everything around the world were the same, why bother traveling in the first place?