No, I think the symbols should be present by default, just a lot smaller than in that screenshot. Ideally you'd have to zoom in a bit to see it better, but you should still be able to select it without problems when zoomed out all the way.
It would be interesting to be able to 'pop up' a bunch of info for a mission, though -- such as terrain, estimated number of enemies, races spotted, number of civilians threatened . . .
Here's an idea, but it may be too elaborate to implement code-wise:
The geoscape doesn't feature individual icons for missions, only 'hotspot' icons on which you can get further information by clicking on them, which pops up a little window in a corner of the geoscape containing the specific mission icon (at a good size) and a short bit of relevant mission information.
Opinions welcome.
Regards,
Winter