I always use a text button labelled "go" or "search" or "find" depending on the specific application and what clicking that button will do. Sometimes if it's a very specific search box I add more to the button such as "find customers" or "search map" or "search for incidents"

Of course I build custom business applications usually for domain experts who, if they don't already, are willing to learn a tool or process if it will help them do their job. This is, of course very different from sites where half a second of confusion can lead to a lost sale or closing the tab.