I feel sorry for Tender Branson. Austria not being on the list must hurt him a lot.
If it is a mission conducted by the European Space Agency, might be an Austrian. He or she will put the blue flag with the circle of yellow stars and the red white red flag on the Mars surface.
The chances for that are very low because there is currently no Austronaut at ESA.
There are 3 Italians, 2 Germans, 1 French, 1 British and 1 Danish active astronauts.
A Mars landing is presumably far enough in the future that it'll probably be none of these people, so Austria still has a chance.