Why would my cat pee on my bed?

Usually when I awake in the morning I get out of bed and come downstairs and the first thing I do is give my two cats a kitty treat. This morning I had a basket of clothes to fold that I was too tired to fold last night so I proceeded to do that instead of coming downstairs first. My cats are sisters but with very different personalities and one is much closer to me than the other. She is the one that jumped up on the corner of the bed and squatted right in front of me and peed just a little circle about the size of a silver dollar. I got the feeling it was to let me know I was doing something different and she didn't like it. I know a lot about cats but this is the first time I've seen this kind of behavior. Do you think it was out of anger or does she maybe have a Urinary Tract Infection?