Woke up to blood stain, possible UTI?

I have two cats, one is a two year old male (orange) and the other is a one year old female (black). They're both spayed/neutered, and they never go outside.

I woke up today to find blood about 7 feet away from the litter box. I dug through it to inspect for blood and found nothing. I'm not sure which of them could have done this. Neither of them were acting lethargic either, they were both as loud as ever, yelling at me for breakfast.

I still and 8 hours left of work, so I can't take them to the vet until then, but does this look like a UTI? I've never had a cat get one, so I have no idea.