A Ros by any other name would drill as neat.

That's the problem with backing into these things. At first, my contribution to the NQSYW was a regiment of mercenaries, MacDuff's Fusiliers, then I started building a 1740's French army for historical games but they were co-opted and sudenly I found myself with a large enough contingent to need a national name, in a hurry. Thus, Rosmark was founded, in the foggy north.

Now what does one call someone from Rosmark?  The "enemy" and former employer of MacDuff's Fusiliers calls us Rosmarkers. There aren't alot of X-mark countries to look at for examples but "mark" is essentially equivalent to "land" so we can also look at the various "x-land" countries for inspiration.

This gives us (in English not in their own native tongues obviously):
Denmark - Danes/Danish
Greenland - Greenlanders/Greenland
Ireland - Irish/Irish
Scotland - Scots/Scottish
England - English/English
Finnland - Finns/Finnish
Switzerland - Swiss/Swiss   

I am somewhat reluctant to add an 's' to 'Ros' as in Scot-Land Land of Scots, Rosmark, Land of the Ross as the double 's' doesn't seem to implie plural but if I insert an "e" it becomes Roses as in Rosmark, Land of Roses. I don't mind the implication that my people and troops smell sweet and are pretty but it would feel odd. The adjecective woyuld be Rosish in any event. I think this is my favorite at the moment but I am throwing open a Poll. Name those people!  Once again, I do not consider myself bound to obey the results but I will take it into consideration. Comments to back up arguments for one or another are encouraged and gain even more weight.