Most garrisons, or even the legion in itself aren't too fond of non members promoting them out of the risk of getting the wrong information spread. So it's not a good idea. If your garrison will be present then you might be able to attend and help out as a supporter for them. But if not, it's best to not try to represent something you aren't a member of yet.
Having a bunch of garrison approved flyers on your table might be alright. Just check with your garrison first.
As for the pictures, feel free to post them either in the Field Training or the NCO section. We don't mind.