Fig. 1: About the (very good!) Swiss Geoportal I came on this icon (1). I thought it was a slider icon. But this was not so.
It means „switch to full-screen mode“. Confusing. With small variations, the full-screen icon is a fairly well-established element. See the examples below.
So I tweeted to Geoportal and alerted about this usability detail. The answer was, that this is defined by the use of the OpenLayers API.
OpenLayers used Character Icons (That’s another discussion!). So, this is the easiest solution:
I am happy that I could help openlayers.org to improve the usability of their product.
The devil is in the detail!