Answer:
Orthodox Jews will generally only eat in Kosher restaurants.
Non-Orthodox Jews who keep kosher will generally only eat vegetarian or certain fish in restaurants.
__________
For Orthodox Jews who only eat kosher, they will only eat in a restaurant that is certified kosher. Kosher restaurants will display their certification to the public. Meat restaurants will have a moshgiach (kashrut supervisor) on staff during operating hours. Dairy restaurants might also but it's not a requirement, most dairy restaurants will have spot inspections.
Some Orthodox Jews will not eat in any restaurant, even if it's certified Kosher.