If you click on thomas.behr's sample graph, you can see in the Properties view that
* the yellow squares with text inside is from Flowchart.
* the ports are additional labels, where the label icon has been set to a yellow rectangle.
It would be great if these were part of the UML palette by default.
If not, it would be great if someone could create a complete UML pallete and export them for us to import.
In the mean time, open the Sample graph, copy the bits you need and paste into your own diagram.