I don’t frankly see any maris ayin issue at all. If I walked past a treif restaurant and saw a frum person inside sitting with some people, I would assume he was on a business meeting and was not eating. If I saw a frum man walk into McDonalds himself, I would assume he was using the bathroom or buying a soda.
Isn’t that what you would assume?
Isn’t maris ayin only when people will think you are doing something wrong?
(Ex. It is maris ayin to wear something which is labeled as a wool/linen blend, but it is not maris ayin to wear a Hugo Boss suit because everyone assumes you had the shaatnez removed.)