The profiles package contains a metaclass Image. A stereotype can contain a set of images.
The attributes of the Image metaclass provide different ways of defining the image associated with the stereotype. I don't go into these details, as how images are provided will depend a lot on the uml modelling tool.
This allows also to change the shapes of an uml metaclass or replace it completely by an image.
It took me some time, but I managed to get an Icon display for an sterotype using papyrus/eclipse.
I defined a stereotype <<memberVIs>> which extends the metaclass Operation.
As LabVIEW users are already used to Icons (e.g. those in the ProjectExplorer), this feature might be really cool to make uml diagrams faster to read (and make uml more widely accepted by the LabVIEW community).