I think that's best. The browser trick is a multi-purpose method that also allows hovering, I think that's unnecessarily complex (and hidden) in a normal case, especially if the application has a toolbar already.

The xterm uses the same icons as the browser does, but it is not part of any spec. So adding a new selection icon doesn't seem like such a bad idea (maybe it could become part of the SDK at some point). Note that I am not 100% sure that a similar icon doesn't already exist.