So, my hunch seemed to be right after all; the pattern on this cup is not called 'Valencia' (contrary to popular belief) – it is Fiesta. In case you're as much of a pottery nerd as me, you might find this piece of information interesting ;-) I also discovered that it is a cup for serving hot chocolate. Extra yummy!
PS! The designer of this cup is Ulla Procopé who worked for Arabia between 1948-1968. She also designed 'Ruska' – the best selling coffee set in the history of Arabia.
If you are looking for Arabia stuff, this web store in Finland (click on link) seem to carry a lot of the stuff. This is where I found the name... while looking for something else, of course.