Icon for "upgrade"

I'm trying to come up with an icon that would be understood to mean "upgrade" - the user should click on that icon if he wants to upgrade his application/subscription/whatever to a "premium" level.

I've searched the web but all I've found were either icons that included the text "upgrade" or icons that I, at least, would not understand to mean "upgrade".

So how can I convey the "upgrade" message with an icon?