1. Open the "Shape Nodes" palette
2. Put the two triangles, one up and the other down
3. Change its colors
4. Flatten them a bit
5. Place them faced by the vertices
6. Select the triangle on the bottom with the right mouse button
7. Select "Convert to label"
8. Select the triangle on the top
9. Press F2 and add some text
10. Select this text and press the right mouse button
11. Press on "Properties"
12.On the Placement section put Model: Sandwitch, Position: South