Have you noticed that some manufacturers are not putting markings on their chip resistors anymore? Why is this happening ? The answer thankfully is simple, they are taking out a step during the manufacturing process. It eliminates time on making them and of course the cost of the screen printing . This will not have any effect on the performance on the part .The smaller surface mount resistors do not usually have a marking in the first place as the area is just to small to print on. The reels they come on are marked with the information you need . This trend will be happening with more manufacturers as more are starting to do this. Also, you can test them for peace of mind with a multi meter if you are buying single parts or if there already on a board. There are plenty of examples on how to do that on youtube with different models .
Below I posted some examples of the change notices from Vishay and Yageo :