If a menu offers a veggie burger, ask "How is it prepared? In the same area or on the same grill as the flesh, perhaps?" If you frequent restaurants that offer Italian cuisines, for the non-flesh pastas, ask "What is the base of the marinara? Cow flesh?" You may be offered a variety of vegetable soup's, but beware, unless you are assured otherwise, they contain chicken or cow stock.
Of course, these are only examples for the wary. I only mention them because from some direct experience of late, I have been introduced to the world of restaurant deception. Indeed, when a menu claims "We have a garden burger for the vegetarians out there," it stands to reason that said food item is free of flesh. If, however, it is prepared on the same surfaces as the various flesh items, or on the grill following the cooking of a piece of cow, the claim being made by the restaurant about a "vegetarian option" is false. They may rationalize - "The heat is so intense anyways" - but these arguments are just that, rationalizations, which may or may not be sound.
We should, therefore, ask questions. Make it known that we take ethics seriously; dishonesty won't be tolerated. Now, for the waiters, they are not at fault. It make's sense that they are unaware of what is occurring. However, the individuals who created the menu and who cook the food are perpetrating a fraud, even if they don't realize it. So let's tell them: "If you want to offer a vegetarian option(s), make it vegetarian."
Can you imagine a restaurant that purported to offer kosher food items that actually prepares food in a manner not consistent with the Jewish tradition? Sure we can imagine it because of the shortcomings of our species, but my point still holds: Many of these restaurants that claim to be vegfriendly haven't considered what this actually means. They are playing to a sort-of tangential niche market without considering the majority of individuals who exist beyond this tiny "market" but who actually compose, and define, the wider segment of this same population.
At the core of this problem we find mere self-interest (and blatant prejudice?): It takes effort to make good on these claims about being vegfriendly; however, we vegetarians and vegans are the minority, in numbers and power, therefore, for most people, it's simply extra effort that doesn't need to be exerted because a) Who's going to find out? and b) Who cares? The same cannot be said about the Jewish population, for example, which is why my example above holds.
We care. Asking questions - moving beyond the welcoming pretense being presented by the restaurant - will say to these people, "I take this seriously and so should you because..." Be gracious, act with prudence and kindness, which will help prevent the often-taken metaphorical steps backward during these kinds of discussions, but ask nonetheless. It's advocacy of an all-important sort. We must continue to move this force, this discourse about social justice, beyond dismissal into dialogue and criticism. This simple action, if done properly, will help.