Holy semantics, Batman!
- Some people will see the color blue as the defining element of that quest icon, call it a blue quest marker, and that is completely fine.
- Some people will see the "+" as the defining element and call it a "plus" quest marker, and that's also fine.
You call it what you want in your head ("Q plus blue" quest marker, "banana spaceship" quest marker, whatever) but use the search terms society wants to use if you need to look something up. No need to control how the next person defines that icon.
...
This is an issue, why? Let's all quietly stop worrying about what the next person wants to call something. I mean, I come from WoW where folks abbreviate stuff by the first and last letter of a word - something that is done nowhere else on Earth and is mind-numbingly incorrect - but if that's what they want to do, that's what they want to do.
(Example: the word 'heroic' often gets abbreviated to 'HC' in WoW. There are no real-world examples of abbreviating like this. Eh, so be it.)