shlishi-
An example of maaras eyin is serving a parve cheeseburger in your home, without placing proof of its parve status on the table. Walking into a treife roadside store is not, since it is well known that there are acceptable reasons to do so (e.g. use the restrooms, purchase a fountain soda/coffee perhaps). Note that I mention roadside as a way of avoiding the issue of a formal restaurant that probably would not allow such use of its premises.