You should have received a bunch of .svg files which are the ThingMarks you will need.
As those are scalable you can print it in any size you want without losing any visible quality.
Those ThingMarks relate to your Experience Server which is currently hosted by R&D.
The ThingMark element in ThingWorx Studio is just a generic placeholder image. You can specify to which of your actual ThingMarks it relates to by changing the "ThingMark" id in its Properties.
Also in Project > Configuration > Experiences > ThingMark you can specify the ThingMark id, that will recognize / load the experience itself.
As an identifier you can use the number as is in the ThingMark filename, for one of mine this would be e.g. 520:1 (note there's a : instead of a - )